Add docs requirements

.github/workflows/requirements.txt

@@ -0,0 +1,9 @@
+mkdocs==1.4.1
+mkdocs-autorefs==0.4.1
+mkdocs-gen-files==0.4.0
+mkdocs-literate-nav==0.5.0
+mkdocs-material==8.5.7
+mkdocs-material-extensions==1.1
+mkdocstrings==0.19.0
+mkdocstrings-python==0.7.1
+mkdocs-macros-plugin==0.7.0