port: fix swapped protocol and port in add usage example
port: fix swapped protocol and port in add usage example

The arguments for `acbuild port add` are `NAME`, `PROTOCOL`, and `PORT`,
but the example provided the latter two in the wrong order.

jonboulle/acbuild,dgonyeo/acbuild,containers/build,joshix/acbuild,joshix/acbuild,jonboulle/acbuild,dgonyeo/acbuild,asbachb/acbuild,appc/acbuild,appc/acbuild,mikeln/acbuild,mikeln/acbuild,asbachb/acbuild,containers/build