DOC: No links to prior versions docs
### 

- [X] I have checked that the issue still exists on the latest versions of the docs on `master` [here](https://pandas.pydata.org/docs/dev/)


### Location of the documentation

https://pandas.pydata.org/docs/index.html

### Documentation problem

It is difficult to access the documentation of prior pandas versions. https://pandas.pydata.org/docs/index.html has no links to prior versions docs or they are difficult to find.

When working with legacy code using older pandas versions, access to the docs of a specific version, especially the API reference, can be useful.

While it if possible to find the URL, e.g. https://pandas.pydata.org/pandas-docs/version/0.24.0/ with a bit of trial and error, a list of links to the prior versions docs would be useful.

### Suggested fix for documentation

Add a page in the docs with a list of links to prior versions docs.