Add examples for join.

README.md

@@ -845,6 +845,12 @@ for rows.Next() {
 }
 
 db.Table("users").Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Scan(&results)
+
+// find a user by email address
+db.Joins("inner join emails on emails.user_id = users.id").Where("emails.email = ?", "x@example.org").Find(&user)
+
+// find all email addresses for a user
+db.Joins("left join users on users.id = emails.user_id").Where("users.name = ?", "jinzhu").Find(&emails)
 ```
 
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