YAML Formatting & Validation (#347)

* leverage yamllint in GitHub actions 

* add pre-commits

* validation updates

* Update README.md

* Update CONTRIBUTING.md

.github/workflows/validation.yml

@@ -1,3 +1,4 @@
+---
 name: Validate definitions
 
 on:
@@ -11,12 +12,14 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
-    - name: Setup Python
-      uses: actions/setup-python@v1
-      with:
-        python-version: 3.6
-    - name: Install dependencies
-      run: pip install -r requirements.txt
-    - name: Run tests
-      run: pytest --tb=line -v
+      - uses: actions/checkout@v1
+      - name: Setup Python
+        uses: actions/setup-python@v1
+        with:
+          python-version: 3.6
+      - name: Install dependencies
+        run: pip install -r requirements.txt
+      - name: Lint YAML files
+        run: yamllint --format parsable --strict -c=tests/yamllint.yaml .
+      - name: Run Device-Type Tests
+        run: pytest --tb=line -v