ci: trigger mdBook build only on relevant docs changes

Author: Athemis

.github/workflows/mdbook.yml

@@ -4,6 +4,9 @@ on:
   # Runs on pushes targeting the default branch
   push:
     branches: ["main"]
+    paths:
+      - "docs/user-guide/**"
+      - ".github/workflows/mdbook.yml"
 
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch: