Add basic documentation

api.py

@@ -1,4 +1,16 @@
 # -*- coding: utf-8 -*-
+#
+# This script parses the README.md and generates a machine-readable
+# data structure from it, for publication as an API.
+#
+# https://springload.github.io/awesome-wagtail/api/v1/readme.json
+#
+# It is automatically ran as part of Travis builds, also validating the README
+# formatting, and the API endpoint is deployed on successful builds on master.
+#
+# See also:
+# - https://djangopackages.org/api/v3/grids/wagtail-cms/
+# - https://github.com/awesomerank/rank
 
 from __future__ import absolute_import, unicode_literals