Copy over context from settings file

Instead of referencing the example externally, we now explain the
setting inline.

lms/envs/common.py

@@ -80,10 +80,22 @@ FEATURES = {
     ## Doing so will cause all courses to be released on production
     'DISABLE_START_DATES': False,  # When True, all courses will be active, regardless of start date
 
-    # When True, will only publicly list courses by the subdomain. Expects you
-    # to define COURSE_LISTINGS, a dictionary mapping subdomains to lists of
-    # course_ids (see dev_int.py for an example)
+    # When True, will only publicly list courses by the subdomain.
     'SUBDOMAIN_COURSE_LISTINGS': False,
+    # Expects you to define COURSE_LISTINGS, a dictionary mapping
+    # subdomains to lists of course_ids
+    # COURSE_LISTINGS = {
+    #     'default': [
+    #         'BerkeleyX/CS169.1x/2012_Fall',
+    #         'HarvardX/CS50x/2012',
+    #         'MITx/3.091x/2012_Fall',
+    #     ],
+    #     'openedx': [
+    #         'BerkeleyX/CS169.1x/2012_Fall',
+    #     ],
+    # }
+    # To see it in action, add the following to your /etc/hosts file:
+    #     127.0.0.1 openedx.dev
 
     # When True, will override certain branding with university specific values
     # Expects a SUBDOMAIN_BRANDING dictionary that maps the subdomain to the