Add modifier suffix example using new {} syntax

Author: guoyao

README.md

@@ -174,7 +174,7 @@ fmt.Printf("%d %q\n", match.Index, match)
 
 #### Modifiers
 
-Modifiers must be placed after the parameter (e.g. `/:foo?`, `/(test)?`, or `/:foo(test)?`).
+Modifiers must be placed after the parameter (e.g. `/:foo?`, `/(test)?`, `/:foo(test)?`, or `{-:foo(test)}?`).
 
 ##### Optional