docs: Don't build certain doc strings for now.

We ran into memory issues at RTD so skip the xmodule, cms and common
docs for now so we can get some of the stuff up.  We can come back to it
later once we make things better.

docs/guides/conf.py

@@ -278,11 +278,14 @@ autodoc_mock_imports = [
 # run sphinx-apidoc against and the directories under "docs" in which to store
 # the generated *.rst files
 modules = {
-    'cms': 'references/docstrings/cms',
     'lms': 'references/docstrings/lms',
     'openedx': 'references/docstrings/openedx',
-    'common': 'references/docstrings/common',
-    'xmodule': 'references/docstrings/xmodule',
+    # Commenting this out for now because they blow up the build
+    # time and memory limits for RTD.  We can come back to these
+    # later once we get parallel builds working hopefully.
+    # 'cms': 'references/docstrings/cms',
+    # 'common': 'references/docstrings/common',
+    # 'xmodule': 'references/docstrings/xmodule',
 }