Docs readme update
- [x] Helps with #23084 
- [x] No tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] Modified the process for updating forks in docs/README.rst to use git merge instead of git rebase. Also added the git command for setting upstream to pandas.

This all seems duplicative of the contributing page. How about we extract what isn't in there already and just change `doc/README.rst` to a link pointing to that? # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23097?src=pr&el=h1) Report
> Merging [#23097](https://codecov.io/gh/pandas-dev/pandas/pull/23097?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c8ce3d01e9ffafc24c6f9dd568cd9eb7e42c610c?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/23097/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23097?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23097   +/-   ##
=======================================
  Coverage    92.2%    92.2%           
=======================================
  Files         169      169           
  Lines       50924    50924           
=======================================
  Hits        46952    46952           
  Misses       3972     3972
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.62% <ø> (ø)` | :arrow_up: |
| #single | `42.3% <ø> (ø)` | :arrow_up: |


------

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23097?src=pr&el=footer). Last update [c8ce3d0...4df506c](https://codecov.io/gh/pandas-dev/pandas/pull/23097?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 +1 on what @TomAugspurger says. I personally wouldn't even bother on having a `README` in `docs/`, but if we have one, I'd just link to the contributing page. I suggested a link to the contributing docs to not break links, but I
assume people don't expect URLs pointing inside the tree of a git repo to
be around forever.

On Fri, Oct 12, 2018 at 4:27 PM Marc Garcia <notifications@github.com>
wrote:

> +1 on what @TomAugspurger <https://github.com/TomAugspurger> says. I
> personally wouldn't even bother on having a README in docs/, but if we
> have one, I'd just link to the contributing page.
>
> —
> You are receiving this because you were mentioned.
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>
 @alexander-l-stone can you update to @TomAugspurger suggestion. Closing as stale. @alexander-l-stone if you want to continue working on it, please reopen or create a new PR, and refer to #23828.