Implement jump flag to check the git ref in nixpkgs repository (#23)

cmd/nixpkgs-url/main.go

@@ -32,6 +32,10 @@ $ nixpkgs-url -version`
 	lastFlag := detectCmd.Bool("last", false, "print git head ref without bumping")
 	targetFlag := detectCmd.Bool("target", false, "print which file will be bumped")
 
+	// Do not call as xdg-open for WSL2, URL will be displayed as a clickable in newer terminals, it is enough
+	// https://github.com/microsoft/WSL/issues/8892
+	jumpFlag := detectCmd.Bool("jump", false, "print reasonable URL for the ref")
+
 	flag.Usage = func() {
 		// https://github.com/golang/go/issues/57059#issuecomment-1336036866
 		fmt.Printf("%s", usage+"\n\n")
@@ -82,15 +86,25 @@ $ nixpkgs-url -version`
 			if err != nil {
 				log.Fatalf("Getting the current version has been failed: %s", err.Error())
 			}
-			fmt.Println(current)
+
+			if *jumpFlag {
+				fmt.Println("https://github.com/NixOS/nixpkgs/commit/" + current)
+			} else {
+				fmt.Println(current)
+			}
+
 			return
 		}
 		last, err := nixurl.GetLastVersion()
 		if err != nil {
 			log.Fatalf("Getting the last version has been failed: %s", err.Error())
 		}
 		if *lastFlag {
-			fmt.Println(last)
+			if *jumpFlag {
+				fmt.Println("https://github.com/NixOS/nixpkgs/commit/" + last)
+			} else {
+				fmt.Println(last)
+			}
 			return
 		}