Adding documentation on using domains and / in taint/label keys; Also clarified…

pkg/kubectl/cmd/label.go

@@ -70,7 +70,8 @@ var (
 	labelLong = templates.LongDesc(i18n.T(`
 		Update the labels on a resource.
 
-		* A label must begin with a letter or number, and may contain letters, numbers, hyphens, dots, and underscores, up to %[1]d characters.
+		* A label key and value must begin with a letter or number, and may contain letters, numbers, hyphens, dots, and underscores, up to %[1]d characters each.
+		* Optionally, the key can begin with a DNS subdomain prefix and a single '/', like example.com/my-app
 		* If --overwrite is true, then existing labels can be overwritten, otherwise attempting to overwrite a label will result in an error.
 		* If --resource-version is specified, then updates will use this resource version, otherwise the existing resource-version will be used.`))
 

pkg/kubectl/cmd/taint.go

@@ -58,6 +58,7 @@ var (
 
 		* A taint consists of a key, value, and effect. As an argument here, it is expressed as key=value:effect.
 		* The key must begin with a letter or number, and may contain letters, numbers, hyphens, dots, and underscores, up to %[1]d characters.
+		* Optionally, the key can begin with a DNS subdomain prefix and a single '/', like example.com/my-app
 		* The value must begin with a letter or number, and may contain letters, numbers, hyphens, dots, and underscores, up to %[2]d characters.
 		* The effect must be NoSchedule, PreferNoSchedule or NoExecute.
 		* Currently taint can only apply to node.`))