4035b6ee7d
add reference to pthread_attr(3), as requested in PR 42871. The text added is different from but based on a suggestion by Matthew Mondor.
$NetBSD: README,v 1.6 2009/04/16 18:37:30 wiz Exp $ When making changes to libpthread, please ensure that libpthread_dbg still compiles. Due to limitations in the current pthread implementation, makecontext(3) and sigaltstack(2) should not be used in programs which link against libpthread (whether threads are used or not). This has been noted in the makecontext(3), sigaltstack(2), and pthread(3) man pages.