5881-Full conversion from rst to md

[thiagogquinto]

Thank you for contributing to Pipenv!

The issue

This PR closes #5881

The fix

This PR implements the changes suggested in the issue mentioned, therefore all the docs associated with the docs are fully in MARKDOWN (.md). About the cli file I did not found a way to make the inclusion like the .rst file, so I saw how it was in the docs in html and wrote it in .md.

The checklist

• Associated issue
• A news fragment in the news/ directory to describe this fix with the extension .bugfix.rst, .feature.rst, .behavior.rst, .doc.rst. .vendor.rst. or .trivial.rst (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.