fix invalid link (#689)

readme.md

@@ -97,7 +97,7 @@ go get -u github.com/tal-tech/go-zero
 
      [Rapid development of microservice systems](https://github.com/tal-tech/zero-doc/blob/main/doc/shorturl-en.md)
 
-     [Rapid development of microservice systems - multiple RPCs](https://github.com/tal-tech/zero-doc/blob/main/doc/bookstore-en.md)
+     [Rapid development of microservice systems - multiple RPCs](https://github.com/tal-tech/zero-doc/blob/main/docs/zero/bookstore-en.md)
 
 1. install goctl