adds workflow to main

.github/workflows/main.yml

@@ -1,9 +1,8 @@
 name: Run mdbook and publish GitHub Pages
 
-# off:
-# on:
-  # push:
-  #   branches: []
+on:
+  push:
+    branches: ["main"]
 
 # Allow only one concurrent deployment, skipping runs queued between the run in-progress and latest queued.
 # However, do NOT cancel in-progress runs as we want to allow these production deployments to complete.