Add database doc about the new oembed.maxwidth field

doc/database/db_oembed.md

@@ -4,6 +4,7 @@ Table oembed
 | Field        | Description                        | Type         | Null | Key | Default             | Extra |
 | ------------ | ---------------------------------- | ------------ | ---- | --- | ------------------- | ----- |
 | url          | page url                           | varchar(255) | NO   | PRI | NULL                |       |
+| maxwidth     | Maximum width passed to Oembed     | int(11)      | NO   | PRI | 0                   |       |
 | content      | OEmbed data of the page            | text         | NO   |     | NULL                |       |
 | created      | datetime of creation               | datetime     | NO   | MUL | 0001-01-01 00:00:00 |       |