out_cloudwatch_logs: add docs for ECR Public

Signed-off-by: Zhonghui Hu <[email protected]>

Author: zhonghui12

pipeline/outputs/cloudwatch.md

@@ -112,6 +112,30 @@ Amazon distributes a container image with Fluent Bit and these plugins.
 
 [github.com/aws/aws-for-fluent-bit](https://github.com/aws/aws-for-fluent-bit)
 
+#### Amazon ECR Public Gallery
+
+[aws-for-fluent-bit](https://gallery.ecr.aws/aws-observability/aws-for-fluent-bit)
+
+Our images are available in Amazon ECR Public Gallery. You can download images with different tags by following command:
+
+```
+docker pull public.ecr.aws/aws-observability/aws-for-fluent-bit:<tag>
+```
+
+For example, you can pull the image with latest version by:
+
+```
+docker pull public.ecr.aws/aws-observability/aws-for-fluent-bit:latest
+```
+
+If you see errors for image pull limits, try log into public ECR with your AWS credentials:
+
+```
+aws ecr-public get-login-password --region us-east-1 | docker login --username AWS --password-stdin public.ecr.aws
+```
+
+You can check the [Amazon ECR Public official doc](https://docs.aws.amazon.com/AmazonECR/latest/public/get-set-up-for-amazon-ecr.html) for more details
+
 #### Docker Hub
 
 [amazon/aws-for-fluent-bit](https://hub.docker.com/r/amazon/aws-for-fluent-bit/tags)