bump ci to test again; use this chance to add notes on this feature

docs/README.md

@@ -17,9 +17,13 @@ git clone --recursive https://github.com/apache/incubator-mxnet.git mxnet
 cd mxnet/docs/build_version_doc
 ./setup_docs_ubuntu.sh
 cd ../../
-make docs USE_OPENMP=1
+make docs USE_OPENMP=1 SPHINXOPTS=-W
 ```
 
+OpenMP speeds things up and will work on Ubuntu if you used the `setup_docs_ubuntu.sh` script.
+The `-W` Sphinx option enforces "warnings as errors". This will help you debug your builds and get them through CI.
+**CI will not let a PR through if it breaks the website.** Refer to the [MXNet Developer wiki's documentation guide](https://cwiki.apache.org/confluence/display/MXNET/Documentation+Guide) for troubleshooting tips.
+
 For more information on each API's documentation dependencies, how to serve the docs, or how to build the full website with each legacy MXNet version, refer to the following links:
 
 * [Dependencies](https://github.com/apache/incubator-mxnet/tree/master/docs/build_version_doc#dependencies) - required before you build the docs