Add warning content to readme

Author: guoyao

README.md

@@ -20,6 +20,11 @@ The first need [Go](https://golang.org/) installed (**version 1.11+ is required*
 $ go get -u github.com/soongo/path-to-regexp
 ```
 
+#### Warning
+
+>*Version 3.2.0, 4.0.0, 4.0.5, 5.0.0 have been removed, please use corresponding version 1.3.2, 1.4.0, 1.4.5, 1.5.0.*
+
+
 ## Usage
 
 ```go