[docs] document how to compile/publish docs (#3296)

CONTRIBUTING.md

@@ -380,3 +380,33 @@ to take effect, they need to be compiled using this command:
 Here's an example as a Github PR with comments that describe what the
 different sections of the code do:
 https://github.com/apache/incubator-superset/pull/3013
+
+## Refresh documentation website
+
+  Every once in a while we want to compile the documentation and publish it.
+  Here's how to do it.
+
+  .. code::
+
+    # install doc dependencies
+    pip install -r dev-reqs-for-docs.txt
+
+    # build the docs
+    python setup.py build_sphinx
+
+    # copy html files to temp folder
+    cp -r docs/_build/html/ /tmp/tmp_superset_docs/
+
+    # clone the docs repo
+    cd ~/
+    git clone https://git-wip-us.apache.org/repos/asf/incubator-superset-site.git
+
+    # copy
+    cp -r /tmp/tmp_superset_docs/ ~/incubator-superset-site.git/
+ 
+    # commit and push to `asf-site` branch
+    cd ~/incubator-superset-site.git/
+    git checkout asf-site
+    git add .
+    git commit -a -m "New doc version"
+    git push origin master