doc: Build command improvement

Co-Authored-By: Tanabe Ken-ichi <nabeken@tknetworks.org>

Author: yongjiajun

README.md

@@ -30,7 +30,7 @@ To build the `spf2ip-go` executable from source, follow these steps:
 
 2.  Build the executable:
     ```bash
-    go build -o spf2ip-go ./cmd/spf2ip-go/main.go
+    go build github.com/HENNGE/spf2ip-go/cmd/spf2ip-go
     ```
     This will create an executable named `spf2ip-go` in the current directory.