new api docs (#626)

docs/api/how_to_contribute.md

@@ -0,0 +1,17 @@
+# Contributing to the API documentation
+
+The openapi schema that is used to render the API documentation is generated automatically. However it
+is possible for the community to contribute to and augment the documentation by editing the files
+located in this (`/docs/api/`) directory.
+
+The contents of these files are joined into the various openapi description fields when the schema file
+is regenerated.
+
+Note that changes to these files won't show up in the documentation until the openapi schema file is 
+regenerated and redeployed.
+
+## Regenerating the schema
+
+```
+python manage.py generateschema > peeringdb_server/static/api-schema.yaml
+```