I wonder if we should also document the post-merge hook some of us are using to detect changes in the requirements on merge and update the venv automatically?

e.g.:
```
$ cat .git/hooks/post-merge
if [ $(git diff HEAD@{1} HEAD --name-only | grep 'requirements/' -c) -ne 0 ]
then
        $VIRTUAL_ENV/bin/pip install --exists-action=w --no-deps --download-cache=/tmp/pip-cache -r requirements/dev.txt
fi
```