DOC: create shared includes for comparison docs, take II
This is a duplicate of https://github.com/pandas-dev/pandas/pull/38771, but instead of defining `:tips:` in a `:suppress:` block, it attempts to tell flake8-rst to ignore those warnings. In other words, only one of these pull requests should be merged; the other can be closed.

- [ ] ~~closes #xxxx~~
- [ ] tests added / passed
- [ ] ~~passes `black pandas`~~
- [ ] ~~passes `git diff upstream/master -u -- "*.py" | flake8 --diff`~~
- [ ] ~~whatsnew entry~~
