add manual workflow trigger

Author: jmunroe

.github/workflows/build_image.yml

@@ -1,11 +1,15 @@
 name: Build and push container image
 
 on:
+  # Trigger the workflow when changes to image/ folder are
+  # pushed to the main branch
   push:
     branches:
       - main
     paths:
-      - 'image/**'
+      - "image/**"
+  # Trigger the workflow manually
+  workflow_dispatch:
 
 jobs:
   build-and-push: