Add an entry in the readme for the isort prequisite

modules/lang/python/README.org

@@ -67,6 +67,9 @@ This module has no direct prerequisites. Here are some of its soft dependencies.
 + ~pyimport~ requires Python's module ~pyflakes~:
   + ~pip install pyflakes~
 
++ ~py-isort~ requires [[https://github.com/timothycrosley/isort][isort]] to be installed:
+  + ~pip install isort~
+
 + Python virtual environments install instructions at:
   + [[https://github.com/pyenv/pyenv][pyenv]]
   + [[https://conda.io/en/latest/][Conda]]