DOC: add button to edit on GitHub
- [x] closes #39859 
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Changes made:
- Added an extension that allows to have a sidebar with extra "Show on GitHub" and "Edit on GitHub" links. Found [here](https://mg.pov.lt/blog/sphinx-edit-on-github.html).
- Modified conf.py to make sure the extension is added and links direct to editable pages.
Hi [mroeschke](https://github.com/mroeschke), would you mind taking a look at this? My fix should have all the links direct-able and I added an extension so it resembles the issue description #39859. This is my first issue so please let me know if there's any convention I'm missing. Also, I said in the issue that I was working on this, but I had a ton of issues building pandas for the first time, so that's why my update is delayed. Thanks in advance! pre-commit.ci autofix Thanks for the PR, but someone is already working on this in https://github.com/pandas-dev/pandas/pull/61956 so closing to let them have a change to finish. But happy to have contributions labeled `good first issue` that doesn't have a linked PR open