Suggest two additions to /usr/src/UPDATING for FreeBSD 10

[Robert Burmeister]

Suggest two additions to /usr/src/UPDATING for FreeBSD 10:

1. Note that PKGNG is required in FreeBSD 10,
     and that functionality of previous port management tools may have change or 
have been removed.

     Details of the changed behavior of specific port management tools,
     when used in conjunction with pkgng, should be noted in /usr/ports/UPDATING.


2. Note that the functionality of /converters/libiconv has been moved into the 
base system in FreeBSD 10,
     and that /converters/libiconv should be deinstalled before recompiling all 
ports after an OS upgrade.