Add more descriptive tool description.

Signed-off-by: Tobias Wolf <[email protected]>
On-behalf-of: SAP <[email protected]>

Author: NotTheEvilOne

src/gardenlinux/oci/__main__.py

@@ -15,7 +15,9 @@
 @click.group()
 def cli() -> None:
     """
-    gl-oci click argument entrypoint
+gl-oci provides functionality to handle OCI containers. It can pull and push
+images from remote repositories as well as handle GardenLinux artifacts, OCI
+image indices and manifests.
 
     :since: 0.7.0
     """