doc: some documentation on the configuration part of the tutorial Trying to make it less obscure on first contact

doc: smarter make file We regenerate the tutorials when needed only

doc: use a symbolic link to point to the tutorial the file was lagging behind a ton.

import: warn about new unstable changesets 'hg import' can add new unstable changesets, for example when invoked with '--hidden' or '--exact', or when the working directory parent already is unstable.