Document redis options: port and unixSocket

[srid]

And certainly explain this as well:

port = 0 disables listening on the TCP port. Setting both is also allowed by redis, in which case it listens on both unixSocket and TCP port. Hence I just display a warning if both are set instead of asserting

services-flake/nix/services/redis.nix

Lines 28 to 32 in 821dbf3

	apply = v:
	lib.warnIf ((config.unixSocket != null) && (v != 0)) ''
	`${name}` is listening on both the TCP port and Unix socket, set `port = 0;` to listen on only the Unix socket
	''
	v;

Originally posted by @shivaraj-bh in #353 (comment)