Re-work Docs and split out README (using MkDocs) (#2894)

* Initial Documentation re-org

* remove testing link from readme

* rewrite quickstart

* get code blocks working across mkdocs and github

* add link to plugins repo

* add link to plugins repo and move readme to plugin template repo

* Add emoji to "Extensibility with Plugins" in readme

Co-authored-by: Reinier van der Leer <github@pwuts.nl>

* Make docs deploy workflow path-selective

* Also run workflow when the workflow is updated

* fix readme links under configuration subfolder

* shrink subheadings in readme

---------

Co-authored-by: Toran Bruce Richards <toran.richards@gmail.com>
Co-authored-by: Reinier van der Leer <github@pwuts.nl>

.github/workflows/documentation.yml

@@ -0,0 +1,26 @@
+name: Docs
+
+on:
+  push:
+    branches: [ stable ]
+    paths:
+      - 'docs/**'
+      - 'mkdocs.yml'
+      - '.github/workflows/documentation.yml'
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-python@v2
+      - run: pip install --upgrade pip && pip install mkdocs mkdocs-gen-files
+      - run: git config user.name 'github-actions[bot]' && git config user.email 'github-actions[bot]@users.noreply.github.com'
+      - name: Publish docs
+        run: mkdocs gh-deploy