[Docs] Document how to build and view the website locally (#21434)

docs/process.md

@@ -170,6 +170,18 @@ You will need the specific sphinx version installed, which you can do using
 need to add `~/.local/bin` to your path, if pip installs to there).
 
 
+### Building and viewing the Website locally
+
+To build the site locally for testing purposes you only need a subset of the
+`update_docs.py` command just mentioned above. Specifically:
+
+1. Run `pip3` to install python dependencies, as described above.
+2. Run `make -C site html`.
+3. Run a local webserver on the outout of that command, e.g.,
+   `python3 -m http.server 8000 -d site/build/html`.
+4. Browse to `http://localhost:8000/` (assuming you use port 8000 as above).
+
+
 ## Updating the `emcc.py` help text
 
 `emcc --help` output is generated from the main documentation under `site/`,