Update README.md (#1509)

change  `ShouldBindXML` to `ShouldBindJSON`

README.md

@@ -557,7 +557,7 @@ func main() {
 	// Example for binding JSON ({"user": "manu", "password": "123"})
 	router.POST("/loginJSON", func(c *gin.Context) {
 		var json Login
-		if err := c.ShouldBindXML(&json); err != nil {
+		if err := c.ShouldBindJSON(&json); err != nil {
 			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 			return
 		}