users-guide: Provide more depth in table-of-contents
users-guide: Provide more depth in table-of-contents

Per Simon's request.

(cherry picked from commit 415b706ceb6fa3be55e7c96d8bafb0e98ce184b1)

GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc