Added missing docs

[BrammyS]

Description

Added missing docs to Color-Chan.Discord.Rest, Color-Chan.Discord.Core, Color-Chan.Discord.Caching
Closed #19

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.