Post 0.5.0 cleanup: provide manager, readme, changelog

[bollwyvl]

• fixes Extension does not provide the manager Token #21
• fixes Release 0.5.0 #17
• updates some CHANGELOG links
• update installation (add conda-forge links, update package name, etc.)
• move area (main vs sidebar) to settings
• bump version to 0.5.1 (nothing backwards-incompatible)

[bollwyvl]

I don't anticipate any other changes, and the lack of the exposed token is blocking some downstream stuff, so will likely cut 0.5.1 (#23) once we merge this 🌈 🦄 🎆 .

[yuvipanda]

Thanks, @bollwyvl!