Getting started doc segment

[FasterSpeeding]

Summary

Add a getting started segment to the docs.

Problem

API references are a lot to take in and go over for someone who's just getting used to the library and a getting started segment can help ease people into it.

Ideal implementation

a getting started segment to the docs or at least on the docs site.

Checklist

• I have searched the issue tracker and have made sure it's not a duplicate.
  If it is a follow up of another issue, I have specified it.

[davfsa]

Probably also good to leave this here, along with the migration that is being worked on in #760, I wanted to setup a neat design that we can later integrate with jekyll (what github pages uses, not my choice) to parse .md files to static pages. This will allow us to add more sections without worrying about all the HTML

This involves making the theme for #808 work nicely with jekyll

[FasterSpeeding]

This could possibly also be a resolution for #815 since we could link to tanjun and lightbulb for slash commands in the actual documentation

[davfsa]

Just to add an idea, we could maybe make use of mdBook to do this instead of making a jekyll theme, which is going to be arguably harder.

This would include some planning, but a "hikari book" might be ideal for this. There we could include different sections for different things

[PythonTryHard]

Related PR: #1522