Add info for how to generate ldoc in gh actions

Help people run the same process themselves.

README.md

@@ -57,3 +57,21 @@ Or a batch file called 'ldoc.bat':
     @echo off
     lua \path\to\ldoc\ldoc.lua %*
 
+
+## Generating LDoc on github
+
+To generate docs for your own lua projects see [doc.yml](.github/workflows/doc.yml).
+
+Instead of `luarocks install --only-deps`, use `luarocks install
+https://raw.githubusercontent.com/lunarmodules/LDoc/master/ldoc-scm-3.rockspec`
+and create your own `doc-site` makefile target that runs `ldoc .` in the
+directory containing your `config.ld`.
+
+Ensure `publish_dir` in your doc.yml is set to the same location as your
+`config.ld`'s `dir` parameter.
+
+After you've pushed that change to master, you'll see the build cycle on your
+commit (an orange dot or green checkmark). When that completes, a repo owner
+needs to enable gh-pages on the repository: Settings > Pages and set "Source" to
+gh-pages and root.
+