updating README to describe how the sphinx documentation site can als…

…o be built locally (on Debian Linux) for faster iteration (without needing to push to GitHub to view the site)

README.md

@@ -45,6 +45,35 @@ The following Githb-Pages-hosted Read the Docs sites have been created by clonin
  * [Python Bootcamp for Science](https://vienneae.github.io/rtd-github-pages/en/master/index.html) ([repo](https://github.com/vienneae/rtd-github-pages/tree/master/docs))
  * [Py4Web Docs](https://nicozanf.github.io/py4web-doc/) ([repo](https://github.com/nicozanf/py4web-doc/tree/master/docs))
 
+# Local Iteration
+
+As shown above, you can simply push your changes to GitHub to update your sphinx documentation website.
+
+However, you can also build the site locally on your computer for faster iteration.
+
+## Linux
+
+To build the site on Debian Linux, first download some dependencies
+
+```
+sudo apt-get update
+sudo apt-get -y install git firefox-esr python3-git python3-sphinx python3-sphinx-rtd-theme
+```
+
+Change into the `docs` directory of this repo and build the sphinx site with `make`
+
+```
+cd rtd-github-pages/docs/
+make clean
+make html
+```
+
+You can view the site (built into the `_build/html/` directory) using firefox
+
+```
+firefox-esr _build/html/index.html
+```
+
 # License
 
 The contents of this repo are dual-licensed. All code is GPLv3 and all other content is CC-BY-SA.