Update README to suggest local-nicknames over ace.core
Update README to suggest local-nicknames over ace.core

Currently we suggest using ace.core to give package aliases.
This is a very heavyweight library that won't compile on any
version of Common Lisp but SBCL.
Instead suggest local-nicknames.
It is implemented by all the major lisp variants.
It's also used in cl_protobufs.

PiperOrigin-RevId: 333291041

qitab/cl-protobufs,qitab/cl-protobufs