Add a comment explaining what ADVANCED_COMPONENT_TYPES should be.

While I'm in there, also fix the comment for ADVANCED_PROBLEM_TYPES.

cms/envs/common.py

@@ -935,6 +935,25 @@ DEFAULT_COURSE_LANGUAGE = "en"
 
 ################ ADVANCED_COMPONENT_TYPES ###############
 
+# These strings are entry-point names from the setup.py of the XBlock.
+# For example:
+#
+#   setup(
+#       name='xblock-foobar',
+#       version='0.1',
+#       packages=[
+#           'foobar_xblock',
+#       ],
+#       entry_points={
+#           'xblock.v1': [
+#               'foobar-block = foobar_xblock:FoobarBlock',
+#           #    ^^^^^^^^^^^^ This is the one you want.
+#           ]
+#       },
+#   )
+#
+# To use this block, add 'foobar-block' to the ADVANCED_COMPONENT_TYPES list.
+
 ADVANCED_COMPONENT_TYPES = [
     'annotatable',
     'textannotation',  # module for annotating text (with annotation table)
@@ -975,17 +994,24 @@ ADVANCED_COMPONENT_TYPES = [
     'edx-reverification-block',
 ]
 
-# Adding components in this list will disable the creation of new problem for those
-# compoenents in studio. Existing problems will work fine and one can edit them in studio
+# Adding components in this list will disable the creation of new problem for
+# those components in Studio. Existing problems will work fine and one can edit
+# them in Studio.
 DEPRECATED_ADVANCED_COMPONENT_TYPES = []
 
-# Specify xblocks that should be treated as advanced problems. Each entry is a tuple
-# specifying the xblock name and an optional YAML template to be used.
+# Specify XBlocks that should be treated as advanced problems. Each entry is a
+# dict:
+#       'component': the entry-point name of the XBlock. See the comment for
+#               ADVANCED_COMPONENT_TYPES for details of where to find this
+#               name.
+#       'boilerplate_name': an optional YAML template to be used.  Specify as
+#               None to omit.
+#
 ADVANCED_PROBLEM_TYPES = [
     {
         'component': 'openassessment',
         'boilerplate_name': None,
-    }
+    },
 ]