DOC: small update to install.rst page
Move some content from the removed content on dependencies from the README (see GH13882)

I was going through the install.rst, and updated some small things, but there was actually no content from README to be moved.

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14115?src=pr) is 85.26% (diff: 100%)

> Merging [#14115](https://codecov.io/gh/pydata/pandas/pull/14115?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

``` diff
@@             master     #14115   diff @@
==========================================
  Files           139        139          
  Lines         50502      50502          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          43063      43062     -1   
- Misses         7439       7440     +1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [be61825...4e54c71](https://codecov.io/gh/pydata/pandas/compare/be61825986ba565bc038beb2f5df2750fc1aca30...4e54c71a22bf1999ca7e90fb82b3d95510d093d9?src=pr)
