Better description for new build method option

Author: seunghun1ee

.github/workflows/stackhpc-container-image-build.yml

@@ -9,7 +9,7 @@ on:
         required: false
         default: ""
       service-group:
-        description: Whether to build images by service group (If false images are built by regex match)
+        description: Use regex input for listing images by service instead of pattern matching
         type: boolean
         required: true
         default: false