Add comments in several hack/verify-*.sh(g-r)

hack/verify-openapi-spec.sh

@@ -14,6 +14,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# This script checks whether updating of OpenAPI specification is needed or not.
+# We should run `hack/update-openapi-spec.sh` if OpenAPI specification is out of
+# date.
+# Usage: `hack/verify-openapi-spec.sh`.
+
 set -o errexit
 set -o nounset
 set -o pipefail