Improve Registering a new Clause Formatter documentation

[phronmophobic]

https://cljdoc.org/d/com.github.seancorfield/honeysql/2.6.1161/doc/extending-honeysql#registering-a-new-clause-formatter

The description of honey.sql/register-clause! doesn't seem to specify the formatter function's return value. An example using honey.sql/register-clause! would also be very helpful.

Here's the extension that I ended up using:

(honey.sql/register-clause!
 :merge-into
 (fn [_ table]
   [(str "MERGE INTO " (honey.sql/format-entity table))])
 :values)

Thanks for the useful library!

[phronmophobic]

Awesome!