Add info on building the docs site

README.md

@@ -4,3 +4,32 @@
 This repository contains the source for NREL's Holistic Modeling - WETO Software Portfolio
 Coordination project. See [nrel.github.io/WETOStack/](https://nrel.github.io/WETOStack/) for
 more information.
+
+## Building the site
+
+The site is built using [Jupyter Book](https://jupyterbook.org/intro.html).
+To build the site, run the following command:
+
+```bash
+pip install -r docs/requirements.txt
+
+jupyter-book build .
+```
+
+After a bit of output, the final lines will point to the location of the main HTML file
+that can be opened in a browser:
+
+```
+The HTML pages are in _build/html.
+
+===============================================================================
+
+Finished generating HTML for book.
+Your book's HTML pages are here:
+    _build/html/
+You can look at your book by opening this file in a browser:
+    _build/html/index.html
+Or paste this line directly into your browser bar:
+    file://<removed>/wetostack/docs/_build/html/index.html
+
+```