Tweak the gitpod environment

.gitpod.yml

@@ -1,6 +1,12 @@
+
 tasks:
   - init: pip install -r requirements.txt
   - command: mkdocs serve
 ports:
   - port: 8000
-    onOpen: open-browser
+    onOpen: notify
+vscode:
+  extensions:
+    - yzhang.markdown-all-in-one
+    - davidanson.vscode-markdownlint
+    - bpruitt-goddard.mermaid-markdown-syntax-highlighting