fix the validate command in the docs

Signed-off-by: dongwenjuan <[email protected]>

Author: dongwenjuan

docs/design/operator-bundle.md

@@ -239,7 +239,7 @@ Flags:
 
 The command for `validate` task is:
 ```bash
-$ ./opm alpha bundle build --tag quay.io/coreos/test-operator.v0.1.0:latest --image-builder docker
+$ ./opm alpha bundle validate --tag quay.io/coreos/test-operator.v0.1.0:latest --image-builder docker
 ```
 
 The `validate` command will first extract the contents of the bundle image into a temporary directory after it pulls the image from its image registry. Then, it will validate the format of bundle image to ensure manifests and metadata are located in their appropriate directories (`/manifests/` for bundle manifests files such as CSV and `/metadata/` for metadata files such as `annotations.yaml`). Also, it will validate the information in `annotations.yaml` to confirm that metadata is matching the provided data. For example, the provided media type in annotations.yaml just matches the actual media type is provided in the bundle image.