Update 0-welcome.yml

.github/workflows/0-welcome.yml

@@ -1,21 +1,9 @@
-name: Step 0, Welcome
-
-# This step triggers after the learner creates a new repository from the template.
-# This workflow updates from step 0 to step 1.
-
-# This will run every time we create push a commit to `main`.
-# Reference: https://docs.github.com/en/actions/learn-github-actions/events-that-trigger-workflows
+name: Post welcome comment
 on:
-  workflow_dispatch:
-  push:
-    branches:
-      - main
-
-# Reference: https://docs.github.com/en/actions/security-guides/automatic-token-authentication
+  pull_request:
+    types: [opened]
 permissions:
-  # Need `contents: read` to checkout the repository.
-  # Need `contents: write` to update the step metadata.
-  contents: write
+  pull-requests: write
 
 jobs:
   # Get the current step to only run the main job when the learner is on the same step.