Fix empty section navigation sidebar and reorganize templates a bit (#471)

* fix section navigation sidebar

The sidebar generation logic in the PyData Sphinx Theme was altered, causing the navigation sidebar to become consistently displayed but always empty.

The `sidebar-nav-bs.html` override was initially added to address a responsive design issue, which has now been effectively resolved by the upstream. Let's remove the override to avoid future breakage.

`sidebar_includehidden` is set to `False` to get rid of the sidebar when its content is empty.

* reposition the project links

Add project-related links in a way that does not override upstream templates.

Author: kuanyili

src/_templates/layout.html

@@ -0,0 +1,15 @@
+{# Displays project-related links. #}
+<ul class="nav justify-content-center">
+  <li class="nav-item">
+    <a class="nav-link" href="https://github.com/common-workflow-language/user_guide/blob/main/CODE_OF_CONDUCT.md">Code of Conduct</a>
+  </li>
+  <li class="nav-item">
+    <a class="nav-link" href="https://github.com/common-workflow-language/user_guide/blob/main/CONTRIBUTING.md">Contributing</a>
+  </li>
+  <li class="nav-item">
+    <a class="nav-link" href="https://github.com/common-workflow-language/user_guide/">Source</a>
+  </li>
+  <li class="nav-item">
+    <a class="nav-link" href="https://github.com/common-workflow-language/user_guide/blob/main/CITATION.md">Cite</a>
+  </li>
+</ul>

src/_templates/project-links.html

@@ -207,6 +207,7 @@
     #     "json_url": json_url,
     #     "version_match": version_match,
     # },
+    "sidebar_includehidden": False,
     "use_edit_page_button": True,
     "navbar_align": "content",
     "navbar_end": [
@@ -219,6 +220,7 @@
     "collapse_navigation": True,
     "show_prev_next": True,
     "footer_start": ["copyright", "sphinx-version"],
+    "footer_center": ["project-links"],
     "footer_end": ["theme-version"],
 }