I migrated our style guide to GitHub just before but did it as a ".md" file in an normal code repo rather than in the GH Wiki:
Comparing both here are some general notes:
* GitHub Wiki doesn't support pull requests, the only options are write permission for all GitHub users or just organisation members. ".md" files inside the code repo works just normal code for pull requests.
* GH Wiki has no email notifications for changes, however there is an ATOM feed.
* GH Wiki has built-in support for a "_Sidebar.md" page, which is how the sidebar works.
* You can fairly easily upload images to GH Wiki by cloning the git repo and adding them, basically the same as you'd do with a code repo.
* GH Wiki has a friendly page editor because it has a markdown toolbar, however I don't think this is a must.
* Both have a preview mode.
* As a organisation member you can edit a ".md" file and commit it directly from the web browser, no need to go through a PR.
* The diff support in code repos is better than the wiki ones because it can show you changes within a line rather than just the whole line.
* GH Wiki supports links to other wiki pages with the "[[Page Name]]" syntax, .md files must use the normal markdown "[Page Name](Page-Name.md)" syntax.
* GH Wiki only has one copy of the docs, so you don't get different docs in each branch. A good thing and a bad thing.
* Cloning the code repo would give everyone an offline copy of the docs, and it would make it easier for people to contribute to the docs when they send a PR for the code because it could be the same PR.
I'd like a bit of discussion on whether we should use GitHub Wiki or Markdown files in the code repo.
P.S. Don't worry about getting the actual work done, I'm happy to finish the migration.