i18n: how_to: add instructions to regenerate translations The wrap value of '76' is determined empirically by checking the total diff after regeneration using wrap values 70 - 90, using 'wc' to find the smallest delta. It also corresponds with the help text of Weblate that says that the default is to 'wrap at 77 characters'.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.