Adds comment saying FORUM_API_KEY must match EDXAPP_COMMENTS_SERVICE_KEY.

Roles shouldn't reach into each others' namespaces, and so this change
intentionally avoids assigning one variable to the other.

playbooks/roles/edxapp/defaults/main.yml

@@ -117,6 +117,7 @@ EDXAPP_LOG_LEVEL: 'INFO'
 EDXAPP_MEMCACHE: [ 'localhost:11211' ]
 EDXAPP_CACHE_COURSE_STRUCTURE_MEMCACHE: "{{ EDXAPP_MEMCACHE }}"
 EDXAPP_COMMENTS_SERVICE_URL:  'http://localhost:18080'
+# EDXAPP_COMMENTS_SERVICE_KEY must match FORUM_API_KEY
 EDXAPP_COMMENTS_SERVICE_KEY:  'password'
 
 EDXAPP_EDXAPP_SECRET_KEY: "DUMMY KEY CHANGE BEFORE GOING TO PRODUCTION"

playbooks/roles/forum/defaults/main.yml

@@ -24,6 +24,7 @@ FORUM_MONGO_URL: "mongodb://{{ FORUM_MONGO_USER }}:{{ FORUM_MONGO_PASSWORD }}@{%
 FORUM_SINATRA_ENV: "development"
 FORUM_RACK_ENV: "development"
 FORUM_NGINX_PORT: "18080"
+# FORUM_API_KEY must match EDXAPP_COMMENTS_SERVICE_KEY
 FORUM_API_KEY: "password"
 FORUM_ELASTICSEARCH_HOST: "localhost"
 FORUM_ELASTICSEARCH_PORT: "9200"