Fix short help with analyzeCmd and diffCmd

Fixes "unknown command" errors when using it as described previously.

Author: blueyed

cmd/analyze.go

@@ -30,7 +30,7 @@ import (
 
 var analyzeCmd = &cobra.Command{
 	Use:   "analyze image",
-	Short: "Analyzes an image: container-diff image",
+	Short: "Analyzes an image: container-diff analyze image",
 	Long: `Analyzes an image using the specifed analyzers as indicated via --type flag(s).
 
 For details on how to specify images, run: container-diff help`,

cmd/diff.go

@@ -35,7 +35,7 @@ var filename string
 
 var diffCmd = &cobra.Command{
 	Use:   "diff image1 image2",
-	Short: "Compare two images: container-diff image1 image2",
+	Short: "Compare two images: container-diff diff image1 image2",
 	Long: `Compares two images using the specifed analyzers as indicated via --type flag(s).
 
 For details on how to specify images, run: container-diff help`,