Include jQuery 3.6.1 to fix the lack of RTD injection

Also includes a fix for the font-size in the RTD injection.

Author: mpilgrem

doc/css/extra.css

@@ -1,3 +1,12 @@
 .hidden-warning {
     display: none
 }
+
+/* The Read the Docs flyout is formatted with a font-size that is 90% of the
+body's. Material for MkDocs has a body font-size that is 0.5rem. This body
+font-size will result in the flyout having a font-size of 0.7rem, consistent
+with the font-size of other elements in the theme.
+*/
+body {
+    font-size: 0.777778rem;
+}

mkdocs.yml

@@ -17,6 +17,9 @@ extra_css:
 - css/extra.css
 extra_javascript:
 - js/searchhack.js
+# Read the Docs requires JQuery for its JavaScript code to inject the flyout
+# menu. Material for MkDocs does not come with JQuery.
+- 'https://code.jquery.com/jquery-3.6.1.min.js'
 
 nav:
 - Home: README.md