add comments back to file

.github/workflows/docker.yml

@@ -1,17 +1,22 @@
 name: Docker Build and Push
-
+# Build & Push builds the simapp docker image on every push to master
+# and pushes the image to https://hub.docker.com/u/provenanceio
 on:
   push:
     branches:
       - main
     tags:
       - "v[0-9]+.[0-9]+.[0-9]+" # Push events to matching v*, i.e. v1.0, v20.15.10
       - "v[0-9]+.[0-9]+.[0-9]+-rc*" # Push events to matching v*, i.e. v1.0-rc1, v20.15.10-rc5
-
+
+# Set concurrency for this workflow to cancel in-progress jobs if retriggered.
+# The github.ref is only available when triggered by a PR so fall back to github.run_id for other cases.
+# The github.run_id is unique for each run, giving each such invocation it's own unique concurrency group.
+# Basically, if you push to a PR branch, jobs that are still running for that PR will be cancelled.
+# But jobs started because of a merge to main or a release tag push are not cancelled.
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
   cancel-in-progress: true
-
 jobs:
   docker:
     runs-on: ubuntu-latest