Use the privacy plugin when building the offline docs

This has the effect of bundling up a bunch of files that would otherwise be
pulled in from the net on the client side. As well as enhancing the viewer's
privacy, it also means that we increase someone's ability to view
documentation locally without the need for any sort of working net
connection.

mkdocs-offline.yml

@@ -2,6 +2,7 @@ INHERIT: mkdocs-common.yml
 
 plugins:
   offline:
+  privacy:
 
 site_dir: docs-offline