[handbook] Replace mergemaster(8) with etcupdate(8)

[Ben Woods]

Hi everyone,

I was hoping I could interest a few people into reviewing a patch I have
submitted for the handbook, to update the handbook "Chapter 23. Updating
and Upgrading FreeBSD" to replace the instructions for using mergemaster(8)
with etcupdate(8).

I would be grateful if people could have a look and give comments /
recommendations for improvements

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=206866

Regards,
Ben

--
From: Benjamin Woods
woodsb02 at gmail.com