Add revision-date plugin to mkdocs gh-pages config

.github/workflows/publish_docs.yml

@@ -17,5 +17,5 @@ jobs:
       - uses: actions/setup-python@v2
         with:
           python-version: 3.x
-      - run: pip install mkdocs-material mkdocs-redirects
+      - run: pip install mkdocs-material mkdocs-redirects mkdocs-git-revision-date-plugin
       - run: mkdocs gh-deploy --force --config-file mkdocs-gh-pages.yml

mkdocs-gh-pages.yml

@@ -4,6 +4,7 @@ site_url: https://hydrusnetwork.github.io/hydrus/
 
 plugins:
   - search
+  - git-revision-date
   - redirects:
       redirect_maps:
         'help/access_keys.md': 'access_keys.md'