Documentation integration (#4653)

* Add documentation under docs/ directory

* Add CI workflow for mkdocs configuration checking

* Add documentation issue template

* update pip-tools?

* Update .gitignore files

* Fix .gitignore rules

* Improve release notes page

* remove references to old repo

.github/workflows/check_docs_config.yaml

@@ -0,0 +1,27 @@
+name: Documentation Config Checks
+
+on:
+  push:
+    branches-ignore:
+      - l10*
+
+  pull_request:
+    branches-ignore:
+      - l10*
+
+jobs:
+
+  mkdocs:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout Code
+        uses: actions/checkout@v2
+      - name: Setup Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.9
+      - name: Run Checks
+        run: |
+          pip install pyyaml
+          python docs/ci/check_mkdocs_config.py