Make manpage mention that -p "pidof PROG" works

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

strace.1

@@ -545,11 +545,8 @@ will respond by detaching itself from the traced process(es)
 leaving it (them) to continue running.
 Multiple
 .B \-p
-options can be used to attach to up to 32 processes in addition to
-.I command
-(which is optional if at least one
-.B \-p
-option is given).
+options can be used to attach to up to 32 processes.
+-p "`pidof PROG`" syntax is supported.
 .TP
 .BI "\-P " path
 Trace only system calls accessing