Move printing the valid resource types to a function

Should be calculated from discovery in the future. Also improve
descriptions on the affected commands.

pkg/kubectl/cmd/explain.go

@@ -32,9 +32,15 @@ import (
 
 var (
 	explainLong = templates.LongDesc(`
-		Documentation of resources.
-
-		` + validResources)
+		List the fields for supported resources
+		
+		This command describes the fields associated with each supported API resource.
+		Fields are identified via a simple JSONPath identifier: 
+		
+			<type>.<fieldName>[.<fieldName>]
+			
+		Add the --recursive flag to display all of the fields at once without descriptions.
+		Information about each field is retrieved from the server in OpenAPI format.`)
 
 	explainExamples = templates.Examples(i18n.T(`
 		# Get the documentation of the resource and its fields
@@ -49,7 +55,7 @@ func NewCmdExplain(f cmdutil.Factory, out, cmdErr io.Writer) *cobra.Command {
 	cmd := &cobra.Command{
 		Use:     "explain RESOURCE",
 		Short:   i18n.T("Documentation of resources"),
-		Long:    explainLong,
+		Long:    explainLong + "\n\n" + cmdutil.ValidResourceTypeList(f),
 		Example: explainExamples,
 		Run: func(cmd *cobra.Command, args []string) {
 			err := RunExplain(f, out, cmdErr, cmd, args)
@@ -65,7 +71,7 @@ func NewCmdExplain(f cmdutil.Factory, out, cmdErr io.Writer) *cobra.Command {
 // RunExplain executes the appropriate steps to print a model's documentation
 func RunExplain(f cmdutil.Factory, out, cmdErr io.Writer, cmd *cobra.Command, args []string) error {
 	if len(args) == 0 {
-		fmt.Fprintf(cmdErr, "You must specify the type of resource to explain. %s\n", validResources)
+		fmt.Fprintf(cmdErr, "You must specify the type of resource to explain. %s\n", cmdutil.ValidResourceTypeList(f))
 		return cmdutil.UsageErrorf(cmd, "Required resource not specified.")
 	}
 	if len(args) > 1 {