Document -X perf in the manpage

Author: stefanor

Misc/python.man

@@ -371,6 +371,8 @@ Set implementation-specific option. The following options are available:
        This helps avoid denial of service attacks when parsing untrusted data.
        The default is sys.int_info.default_max_str_digits.  0 disables.
 
+    -X perf: support the Linux "perf" profiler; also PYTHONPERFSUPPORT=1
+
 .TP
 .B \-x
 Skip the first line of the source.  This is intended for a DOS