docs: update readme

Author: axetroy

README.md

@@ -151,7 +151,7 @@ $ whatchanged --help
 4. Build and install from source using [Golang](https://golang.org) (All platforms)
 
 ```bash
-go install github.com/whatchanged-community/whatchanged@0.4.0
+go install github.com/whatchanged-community/whatchanged@v0.4.0/cmd/whatchanged
 ```
 
 ### FAQ

README_zh-CN.md

@@ -151,7 +151,7 @@ $ whatchanged --help
 1. 使用 [Golang](https://golang.org) 从源码中构建并安装 (全平台支持)
 
 ```bash
-go install github.com/whatchanged-community/whatchanged@0.4.0
+go install github.com/whatchanged-community/whatchanged@v0.4.0/cmd/whatchanged
 ```
 
 ### 常见问题