GetFile () is the information that users get to upload pictures
func (c *Controller) GetFile(key string) (multipart.File, *multipart.FileHeader, error)
A total of three parameters are returned: the first parameter FileName (file name), the second parameter FileHeader (file header information, including file size, etc.) The third parameter is error
When using the GetFile () function, add an attribute to the form form, enctype = "multipart / form-data", otherwise an error will be reported:
例如：<form method="post" action="/addArticle" enctype="multipart/form-data">