WIP: Start the documentation for Wiki

Are there points in the code the reviewer needs to double check?

This is my first time contributing to GitLab Documentation, so double check everything, sorry.

I am thinking there should be a main page with just the Getting Started and then links to the other pages. Or should this main page have just links, even to Getting Started?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

This is the first step working on #7028 (closed)

What does this MR do?

Add the beginnings of documentation for Wiki's

/cc @axil, @rspeicher, @dblessing (It said to ping all of you when I create a new file in the Docs)