Help users get started after initializing

Update the output of `ghasum init` to include some next steps for what
to do once ghasum is done initializing. This hopefully makes it clearer
to users how to use `ghasum`. Also, it provides some guidelines for how
to improve this command in the future - if (some of) these steps can
automated it would be helpful for the user if they don't have to do it
themselves.

Author: ericcornelissen

cmd/ghasum/init.go

@@ -75,7 +75,11 @@ func cmdInit(argv []string) error {
 		return errors.Join(errUnexpected, err)
 	}
 
-	fmt.Println("Ok")
+	fmt.Println(`Ok
+
+Next:
+1. Track .github/workflows/gha.sum with git.
+2. Integrate ghasum into the project's workflows.`)
 	return nil
 }