Add comments in several hack/*.sh

hack/run-in-gopath.sh

@@ -15,9 +15,10 @@
 # limitations under the License.
 
 # This script sets up a temporary Kubernetes GOPATH and runs an arbitrary
-# command under it.  Go tooling requires that the current directory be under
+# command under it. Go tooling requires that the current directory be under
 # GOPATH or else it fails to find some things, such as the vendor directory for
 # the project.
+# Usage: `hack/run-in-gopath.sh <command>`.
 
 set -o errexit
 set -o nounset