Document PYTHON_CPU_COUNT in the manpage

Author: stefanor

Misc/python.man

@@ -607,6 +607,11 @@ information.
 Setting to 0 disables.
 .IP
 See also the \fB\-X perf_jit\fR option.
+.IP PYTHON_CPU_COUNT
+If this variable is set to a positive integer, it overrides the return
+values of \fIos.cpu_count\fR and \fIos.process_cpu_count\fR.
+.IP
+See also the \fB\-X cpu_count\fR option.
 .IP PYTHONASYNCIODEBUG
 If this environment variable is set to a non-empty string, enable the debug
 mode of the asyncio module.