code: func Edit(c *gin.Context) {
  	db := c.MustGet("db").(*mgo.Database)
  	article := models.Article{}
  	oID := bson.ObjectIdHex(c.Param("_id"))
  	err := db.C(models.CollectionArticle).FindId(oID).One(&article)
  	if err != nil {
  		c.Error(err)
  	}
  
  	c.HTML(http.StatusOK, "articles/form", gin.H{
  		"title":   "Edit article",
  		"article": article,
  	})
  }
docs: // Edit an article