ENH: Add treebeard GitHub Action configuration

Co-authored-by: alex-treebeard <alex@treebeard.io>
Co-authored-by: Rabscuttler <laurence.watson@gmail.com>

Author: 3 people

.github/workflows/notebook-test.yml

@@ -0,0 +1,18 @@
+name: Integration tests
+
+on: [push,pull_request]
+
+jobs:
+  run:
+    runs-on: ubuntu-latest
+    name: Run notebooks on treebeard
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+      - uses: treebeardtech/treebeard@master
+        with:
+          docker-username: thewtex
+          docker-password: "${{ secrets.DOCKER_PASSWORD }}"
+          docker-image-name: insighttoolkit/itkwidgets
+          notebooks:
+            - examples/3DImage.ipynb