DOC: Add more documentation showcasing CalendarDay
xref https://github.com/pandas-dev/pandas/pull/22288#issuecomment-419572535

Highlighting usages of `CalendarDay` with `date_range` and `resample` specifically.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22633?src=pr&el=h1) Report
> Merging [#22633](https://codecov.io/gh/pandas-dev/pandas/pull/22633?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/996f361f8e6986ea1c65ccb164a4c585e1f4a027?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22633/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22633?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #22633   +/-   ##
=======================================
  Coverage   92.16%   92.16%           
=======================================
  Files         169      169           
  Lines       50708    50708           
=======================================
  Hits        46734    46734           
  Misses       3974     3974
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.57% <ø> (ø)` | :arrow_up: |
| #single | `42.35% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22633?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/22633?src=pr&el=footer). Last update [996f361...3da2c7d](https://codecov.io/gh/pandas-dev/pandas/pull/22633?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @mroeschke! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/tests/arrays/categorical/test_constructors.py`](https://github.com/mroeschke/pandas/blob/3b8c102504e68d6188502c11d867fdd8570ac716/pandas/tests/arrays/categorical/test_constructors.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/multi/test_partial_indexing.py`](https://github.com/mroeschke/pandas/blob/3b8c102504e68d6188502c11d867fdd8570ac716/pandas/tests/indexes/multi/test_partial_indexing.py) !

 - There are no PEP8 issues in the file [`pandas/tests/io/formats/test_format.py`](https://github.com/mroeschke/pandas/blob/3b8c102504e68d6188502c11d867fdd8570ac716/pandas/tests/io/formats/test_format.py) !

 - There are no PEP8 issues in the file [`pandas/tests/test_multilevel.py`](https://github.com/mroeschke/pandas/blob/3b8c102504e68d6188502c11d867fdd8570ac716/pandas/tests/test_multilevel.py) !

 - There are no PEP8 issues in the file [`pandas/tests/test_resample.py`](https://github.com/mroeschke/pandas/blob/3b8c102504e68d6188502c11d867fdd8570ac716/pandas/tests/test_resample.py) !

 - There are no PEP8 issues in the file [`pandas/tests/test_window.py`](https://github.com/mroeschke/pandas/blob/3b8c102504e68d6188502c11d867fdd8570ac716/pandas/tests/test_window.py) !

 Closing as we're not moving forward with "CD"