evolve: document the "if not shouldupdate" block
I missed the "not" in "if not shouldupdate: ... hg.updaterepo()" and
it took a long time for me to realize it's about updating *back* to
the original commit (or to its successor). Let's add a comment to
maybe help the person not make the same mistake.
syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
^tests/.*\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes
^docs/training/graphs/
^docs/training/html/
^docs/training/index.html
^docs/training/graphviz-images/
^docs/training/img/
^docs/training/output/
^docs/training/pandocfilters/