Use `edit_uri` correctly in mkdocs.yml

[DiscoStarslayer]

According to the documentation we are not correctly using edit_uri. Currently we set this config to a full path (https://github.com/xqemu/xqemu.com/blob/master/docs/) because our docs live in a separate repo from the project we are documenting (https://github.com/xqemu/xqemu/).

This is incorrect, as edit_uri is only meant to be a path that is appended to the repo_url, not a separate route entirely. Our current use of this property is not expected by the documentation and may break in the future.

We should ideally fix this problem, depending on the end result of #41.

No GitHub link on top-right of the page:

• Change repo_url to point to this project (https://github.com/xqemu/xqemu.com/)

Keep GitHub link on the top-right of the page:

• Investigate a plugin to extend repo_url and edit_uri to allow greater customization. See relevant plugin hook here