Move 'For Developers' content from wiki to contributing docs.
Content from the 'For Developers' content section of the wiki should be included in the pandas documentation where relevant. 

- [ ] Code Style and Conventions
- [ ] Testing #20501
- [ ] Documenting new features and bug fixes
- [ ] Using Git
- [ ] Choosing Exceptions to Raise
- [ ] Tips & Tricks for pandas dev
- [ ] A quick overview of pandas.util
- [ ] Git Workflows
- [ ] Pandas Development FAQ
- [ ] Building On Windows

PRs welcome for any of the above sections.