Add docs theme toggle and update requirements.txt

mkdocs/requirements.txt

@@ -1,4 +1,8 @@
 # Direct dependencies
-mkdocs==1.1.2
-mkdocs-material==6.1.0
-mkdocs-git-revision-date-localized-plugin==0.7.3
+mkdocs>=1.1
+Pygments>=2.4
+markdown>=3.2
+pymdown-extensions>=7.0
+mkdocs-material-extensions>=1.0
+mkdocs-git-revision-date-localized-plugin>=0.7.3
+mkdocs-material>=6.1.0