🚧 Add image tag to step summary

.github/workflows/ci.release.md

@@ -0,0 +1,18 @@
+Use the image built **for this branch** in Nextstrain CLI:
+
+    NEXTSTRAIN_DOCKER_IMAGE=docker.io/nextstrain/base:${TAG}
+
+Note that this isn't always the image built for this CI run, as it will be
+updated on new pushes to the branch.
+
+<!---
+TODO: Add instructions to use image built for this specific CI run. Not trivial
+since it requires getting the SHA for each platform variant. Something like
+this gets that info but is hacky:
+
+    image=nextstrain/base
+    tag=latest
+    token=$(curl --silent "https://auth.docker.io/token?scope=repository:$image:pull&service=registry.docker.io"  | jq -r '.token')
+    curl -s --header "Accept: application/vnd.docker.distribution.manifest.list.v2+json" --header "Authorization: Bearer ${token}" "https://registry-1.docker.io/v2/$image/manifests/$tag" | jq -r '.manifests|.[]| "\(.digest) \(.platform.architecture) \(.platform.variant)"'
+
+--->

.github/workflows/ci.yml

@@ -77,6 +77,7 @@ jobs:
 
     outputs:
       tag: ${{ env.TAG }}
+      digest: 
 
   # Run tests with the final image from GitHub Container Registry.
   test:
@@ -198,6 +199,19 @@ jobs:
       run: |
         ./devel/copy-images -i ghcr.io -o docker.io -t ${{ needs.build.outputs.tag }} -l
 
+  push-summary:
+    needs: [build, push-branch, push-build]
+    runs-on: ubuntu-latest
+    steps:
+    - name: Generate summary
+      run: |
+        # Replace ${x} in Markdown with value of environment variable "x".
+        perl -pe 's/\$\{(.+?)\}/$ENV{$1}/ge' \
+          < .github/workflows/ci.release.md \
+          > "$GITHUB_STEP_SUMMARY"
+      env:
+        TAG: ${{ needs.build.outputs.tag }}
+
   # Run pathogen repo CI builds with the final image
   test-pathogen-repo-ci:
     # Only one of push-{branch,build} runs for any given workflow run, and