include instructions to preview changes in CONTRIB

CONTRIBUTING.md

@@ -6,6 +6,28 @@ see:
 
 http://docs.python-guide.org/en/latest/notes/contribute/
 
+How to test your changes
+------------------------
+
+The html version of this guide is built with [sphinx](http://www.sphinx-doc.org/en/stable/). You may test your revisions locally by having sphinx installed. You can do this easily with pip (as described in the link).
+
+``` bash
+pip install --user sphinx
+```
+
+Then navigate to the directory of the makefile and ```make build``` or ```make html```. Sphinx will then generate the html in a folder called _build/html
+
+After navigating to this folder, you can then use python's built in webserver to view your changes locally:
+
+``` bash
+python3 -m http.server
+```
+
+By default, http.server listens on every ip address bound on your host on port 8000. To bind to a specific one, say, localhost on port 8005:
+
+``` bash
+python3 -m http.server 8005 --bind 127.0.0.1
+```
 
 Style Guide
 -----------