Add markdown linter to format check

.github/workflows/formatting_check.yml

@@ -7,5 +7,6 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: paolorechia/pox@v1.0.1
+      - uses: actionshub/markdownlint@main
         with:
           tox_env: "format_check"

.markdown_style.rb

@@ -0,0 +1,3 @@
+all
+exclude_tag :line_length
+rule 'MD007', :indent => 4

tox.ini

@@ -17,9 +17,11 @@ deps =
     isort
     black
 skip_install = True
+allowlist_externals = mdl
 commands =
     isort bdfr tests --check
     black bdfr tests --line-length 120 --check
+    mdl README.md docs/ -s .markdown_style.rb
 
 [isort]
 profile = black