Update README.md - fix example as per @cmoulliard's suggestion

Author: jessebot

README.md

@@ -52,7 +52,7 @@ spec:
   generators:
     - plugin:
         configMapRef:
-          name: secret-plugin-generator
+          name: secret-var-plugin-generator
         input:
           parameters:
             secret_vars: ["app_name"]