Update workflow-syntax-for-github-actions.md

Author: varunsridharan

content/actions/reference/workflow-syntax-for-github-actions.md

@@ -542,7 +542,7 @@ jobs:
         uses: docker://alpine:3.8
 ```
 
-##### Example using a Docker public registry action
+##### Example using a Github Container Registry
 
 `docker://{host}/{image}:{tag}`
 
@@ -556,6 +556,20 @@ jobs:
         uses: docker://ghcr.io/cloud-builders/gradle
 ```
 
+##### Example using a Docker public registry action
+
+`docker://{host}/{image}:{tag}`
+
+A Docker image in a public registry - <sub>[Google Container Registry - GCR](https://cloud.google.com/container-registry)</sub>
+
+```yaml
+jobs:
+  my_first_job:
+    steps:
+      - name: My first step
+        uses: docker://gcr.io/cloud-builders/gradle
+```
+
 #### **`jobs.<job_id>.steps.run`**
 
 Runs command-line programs using the operating system's shell. If you do not provide a `name`, the step name will default to the text specified in the `run` command.