DOC: split Contributing page
#### Location of the documentation

https://pandas.pydata.org/docs/development/contributing.html

#### Documentation problem

The page is long and covers a lot:

- Environment setup
- The mechanics of contributing to code and docs
- Code standards

#### Suggested fix for documentation

I suggest streamlining the primary Contributing page to be about the basic workflow, splitting out sub-pages for:

- Setting up an environment outside of Docker
   - `Installing a C compiler`
   - `Creating a Python environment`
   - `Creating a Python environment (pip)`
- `Contributing to the code base`
- `Contributing to the documentation`