CustomQueryPart manual section should explain how to implement accept()

[lukaseder]

In jOOQ 3.8, we changed the internals, no longer allowing CustomQueryPart implementations to override toSQL() and bind(), but require them to implement accept() instead: #3323

The change has been "announced" already in jOOQ 3.4 through deprecation of toSQL() and bind():
https://www.jooq.org/javadoc/3.4.0/org/jooq/impl/CustomQueryPart.html

This change has not yet been documented, however:
https://www.jooq.org/doc/3.11/manual/sql-building/queryparts/custom-queryparts

jOOQ manuals 3.4+ should use accept(), not toSQL() and bind()