execve.2: point to exec(3) early

execve.2: point to exec(3) early

Most people actually want exec(3) (or one of its aliases);
the minutiae are a separate, rarer, concern, and execve(2) hijacks
man execve from all the other exec(3) aliases
(similarly to exec(1posix), but it's at least obvious in that case that
 you got the wrong page)

Reported-in: https://twitter.com/NireBryce/status/1529538043039850499
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>