feat(ci): add action to test the build (#147)

Prevent the merge of PR that raises errors and warning.
On some pages, there are errors that are preventing to correctly display the page.

Author: gsanchietti

.github/workflows/test-build.yml

@@ -0,0 +1,15 @@
+name: "Pull Request Docs Check"
+on: 
+- pull_request
+- workflow_dispatch
+
+jobs:
+  docs:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - uses: ammaraskar/sphinx-action@master
+      with:
+        docs-folder: "."
+        pre-build-command: "pip install -r requirements.txt"
+        build-command: "sphinx-build -W --keep-going . _build "