Add entry for `entr` as a generic way to add re-compile support on Unix environments

[Armando Pérez Marqués]

The site http://entrproject.org/ has a few of examples, and here's how I use it personally:

find my_app/ -name \*.py | entr -r python -m my_app serve

Where the command python -m my_app serve launches a generic Python Web server (framework independent).