Update beego.md

Author: myzero1

beego.md

@@ -49,3 +49,20 @@ func (c *MigrationsController) GetOne() {
 ......
 
 ```
+
+
+##### model的example
+```
+
+......
+type Migrations struct {
+	Id                 int       `orm:"column(id_migration);auto" description:"surrogate key:735" example:"735"`
+	Name               string    `orm:"column(name);size(255);null" description:"migration name, unique"`
+	CreatedAt          time.Time `orm:"column(created_at);type(timestamp);auto_now_add" description:"date migrated or rolled back"`
+	Statements         string    `orm:"column(statements);null" description:"SQL statements for this migration"`
+	RollbackStatements string    `orm:"column(rollback_statements);null" description:"SQL statment for rolling back migration"`
+	Status             string    `orm:"column(status);null" description:"update indicates it is a normal migration while rollback means this migration is rolled back"`
+}
+......
+
+```