Document that gettimeofday() is obsolescent
Reported by: kaktus
I am not sure if I should put the link to this document in the commit message:
Also, the POSIX standard I specified in the manual is rendered as `IEEE Std 1003.1-2008 (“POSIX.1”)`. I am not sure if this is good enough (the website mentions `IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)`).