docs: Truncate pages, point users to GitLab repo
Truncates all but one of the *.md files in this repo, and links out to their replacements in the gitlab repo.
I'm adding more than the usual number of reviewers because I don't want this change to come as a surprise to anyone. The pages were copied over in the merge requests attached to Move Shell documentation into the main develope... (#596 - closed) and this merge request tidies up the orphaned files left behind.
- Adding @j.seto because he was slated to be the reviewer of these pages.
- Adding @tlinz and @sean_carroll because PM / EM.
- CC'ing @igor.drozdov because he wanted to make a change to one of these pages this morning, thus my realization that I needed to finish up the work ASAP.