Rendering Methods portions of #24024
Uses Substitution for the strftime docstring instead of pinning it below the method.

Changes section titles from "Formatting" to "Rendering Methods" to match other classes.

This is a pre-requisite to another push I'm making to split less-trivial pieces off of #24024, figured it was a decent small-scope to get out of the way.
Hello @jbrockmendel! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/arrays/datetimelike.py`](https://github.com/jbrockmendel/pandas/blob/431a90c9cb4353962ebfaf5c99c9989d70bfb495/pandas/core/arrays/datetimelike.py) !

 - There are no PEP8 issues in the file [`pandas/core/arrays/datetimes.py`](https://github.com/jbrockmendel/pandas/blob/431a90c9cb4353962ebfaf5c99c9989d70bfb495/pandas/core/arrays/datetimes.py) !

 - There are no PEP8 issues in the file [`pandas/core/arrays/period.py`](https://github.com/jbrockmendel/pandas/blob/431a90c9cb4353962ebfaf5c99c9989d70bfb495/pandas/core/arrays/period.py) !

 - There are no PEP8 issues in the file [`pandas/core/arrays/timedeltas.py`](https://github.com/jbrockmendel/pandas/blob/431a90c9cb4353962ebfaf5c99c9989d70bfb495/pandas/core/arrays/timedeltas.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=h1) Report
> Merging [#24392](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8c58817bd0eaca46d7c0d0c975715ad37fe43710?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `58.82%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24392/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24392      +/-   ##
==========================================
- Coverage    92.3%   92.29%   -0.02%     
==========================================
  Files         162      162              
  Lines       51875    51884       +9     
==========================================
+ Hits        47883    47885       +2     
- Misses       3992     3999       +7
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.7% <58.82%> (-0.02%)` | :arrow_down: |
| #single | `42.99% <47.05%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/arrays/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/24392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3BlcmlvZC5weQ==) | `98.49% <100%> (-0.01%)` | :arrow_down: |
| [pandas/core/arrays/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/24392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lcy5weQ==) | `97.73% <25%> (-0.52%)` | :arrow_down: |
| [pandas/core/arrays/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/24392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3RpbWVkZWx0YXMucHk=) | `86.63% <40%> (-0.53%)` | :arrow_down: |
| [pandas/core/arrays/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/24392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lbGlrZS5weQ==) | `96.31% <85.71%> (-0.21%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=footer). Last update [8c58817...b355220](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=h1) Report
> Merging [#24392](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8c58817bd0eaca46d7c0d0c975715ad37fe43710?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `58.82%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24392/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24392      +/-   ##
==========================================
- Coverage    92.3%   92.29%   -0.02%     
==========================================
  Files         162      162              
  Lines       51875    51884       +9     
==========================================
+ Hits        47883    47885       +2     
- Misses       3992     3999       +7
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.7% <58.82%> (-0.02%)` | :arrow_down: |
| #single | `42.99% <47.05%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/arrays/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/24392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3BlcmlvZC5weQ==) | `98.49% <100%> (-0.01%)` | :arrow_down: |
| [pandas/core/arrays/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/24392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lcy5weQ==) | `97.73% <25%> (-0.52%)` | :arrow_down: |
| [pandas/core/arrays/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/24392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3RpbWVkZWx0YXMucHk=) | `86.63% <40%> (-0.53%)` | :arrow_down: |
| [pandas/core/arrays/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/24392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lbGlrZS5weQ==) | `96.31% <85.71%> (-0.21%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=footer). Last update [8c58817...b355220](https://codecov.io/gh/pandas-dev/pandas/pull/24392?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @jbrockmendel 