version-control/cheet-sheet.md: Add a generic outline for the cheat sheet
version-control/git/cheet-sheet.md: Add a Git-specific cheat sheet
version-control/svn/cheet-sheet.md: Add a Subversion-specific cheat sheet

I pulled commands out of the README.md as they were added to the cheat
sheet.
version-control/git: Use git-and-github notes

Consolidate on these instructor notes because they are already in a
condensed format.  Remove the long-form local/remote READMEs, whose
content should be merged into the instructor guide.  Flesh out the
cheat sheet with additional commands mentioned in the new instructor
notes.