Documentation: Include notes on mapping ports

When mapping ports as strings there is an issue with the way YAML parses
numbers in the format "xx:yy" where yy is less than 60 - this issue is
now included in the documentation.

This fixes #103

docs/django.md

@@ -29,14 +29,14 @@ Simple enough. Finally, this is all tied together with a file called `fig.yml`.
     db:
       image: orchardup/postgresql
       ports:
-        - 5432
+        - "5432"
     web:
       build: .
       command: python manage.py runserver 0.0.0.0:8000
       volumes:
         - .:/code
       ports:
-        - 8000:8000
+        - "8000:8000"
       links:
         - db