Markdown lint (#58)

* markdown linter

* format markdown docs

* format exiting markdown docs

.github/workflows/markdown.yml

@@ -0,0 +1,22 @@
+name: Markdown linter
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+
+  linter:
+    name: markdown linter
+    runs-on: ubuntu-latest
+    steps:
+    
+    - name: Check out code
+      uses: actions/checkout@v2
+    
+    - name: Markdown Linting Action
+      uses: avto-dev/markdown-lint@v1.3.1
+      with:
+        args: 'find . -name "*.md"'