Convert the repository homepage to an overview tab #1855

This might be a bit much for Refined GitHub, but it would be cool if repository homepages were more of a stripped-down overview:

Then, the “Code” tab could link to https://github.com/:user/:repo/tree/:default_branch and display just the code:

This mirrors the behavior of the mobile version of the site, except it takes advantage of the extra available space on desktop computers to show the entire README instead of an excerpt. This also creates an opportunity to display more information on the repository overview page.

The /tree/:default-branch page currently looks identical to the repo homepage.

What do you think?