DOC: timeseries.rst floating point precision (#15817)
 - [x] closes #15817
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15919?src=pr&el=h1) Report
> Merging [#15919](https://codecov.io/gh/pandas-dev/pandas/pull/15919?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/3b53202d90e86a1bc0f5db7a9c2e66c164f909a9?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/15919/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/15919?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #15919      +/-   ##
==========================================
- Coverage   90.97%   90.96%   -0.01%     
==========================================
  Files         145      145              
  Lines       49475    49475              
==========================================
- Hits        45008    45007       -1     
- Misses       4467     4468       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.72% <ø> (-0.01%)` | :arrow_down: |
| #single | `40.68% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15919?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/tseries/tools.py](https://codecov.io/gh/pandas-dev/pandas/pull/15919?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvdG9vbHMucHk=) | `85.55% <ø> (ø)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/15919?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `90.68% <0%> (-0.35%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15919?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/15919?src=pr&el=footer). Last update [3b53202...7b82e8b](https://codecov.io/gh/pandas-dev/pandas/pull/15919?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). I've moved the warning in `to_datetime` to examples and rearranged sections in `timeseries.rst` to make it more logical (IMO). lgtm. @jorisvandenbossche  thanks!