DOC: Improved README formatting.
Fixed a couple of minor inconsistencies in the formatting of the CheatSheet README file.

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25808?src=pr&el=h1) Report
> Merging [#25808](https://codecov.io/gh/pandas-dev/pandas/pull/25808?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/fbe25233345b750031911f0d4b0845fa115c4432?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/25808/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25808?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25808   +/-   ##
=======================================
  Coverage   91.27%   91.27%           
=======================================
  Files         173      173           
  Lines       53002    53002           
=======================================
  Hits        48375    48375           
  Misses       4627     4627
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.83% <ø> (ø)` | :arrow_up: |
| #single | `41.77% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25808?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/25808?src=pr&el=footer). Last update [fbe2523...e5086fe](https://codecov.io/gh/pandas-dev/pandas/pull/25808?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/25808?src=pr&el=h1) Report
> Merging [#25808](https://codecov.io/gh/pandas-dev/pandas/pull/25808?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/fbe25233345b750031911f0d4b0845fa115c4432?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/25808/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25808?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25808   +/-   ##
=======================================
  Coverage   91.27%   91.27%           
=======================================
  Files         173      173           
  Lines       53002    53002           
=======================================
  Hits        48375    48375           
  Misses       4627     4627
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.83% <ø> (ø)` | :arrow_up: |
| #single | `41.77% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25808?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/25808?src=pr&el=footer). Last update [fbe2523...e5086fe](https://codecov.io/gh/pandas-dev/pandas/pull/25808?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks!