Add a redirect sample for POST method (#2389)

* Add a redirect sample for POST method

Refer to issue https://github.com/gin-gonic/gin/issues/444

* put an empty line before 1396

Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>

README.md

@@ -1394,6 +1394,12 @@ r.GET("/test", func(c *gin.Context) {
 })
 ```
 
+Issuing a HTTP redirect from POST. Refer to issue: [#444](https://github.com/gin-gonic/gin/issues/444)
+```go
+r.POST("/test", func(c *gin.Context) {
+	c.Redirect(http.StatusFound, "/foo")
+})
+```
 
 Issuing a Router redirect, use `HandleContext` like below.