put PYTHONIOENCODING in man page

Misc/python.man

@@ -384,9 +384,18 @@ files).
 .IP PYTHONINSPECT
 If this is set to a non-empty string it is equivalent to specifying
 the \fB\-i\fP option.
+.IP PYTHONIOENCODING
+If this is set before running the interpreter, it overrides the encoding used
+for stdin/stdout/stderr, in the syntax
+.IB encodingname ":" errorhandler
+The
+.IB errorhandler
+part is optional and has the same meaning as in str.encode. For stderr, the
+.IB errorhandler
+ part is ignored; the handler will always be \'backslashreplace\'.
 .IP PYTHONNOUSERSITE
-If this is set to a non-empty string it is equivalent to specifying
-the \fB\-s\fP option (Don't add the user site directory to sys.path).
+If this is set to a non-empty string it is equivalent to specifying the
+\fB\-s\fP option (Don't add the user site directory to sys.path).
 .IP PYTHONUNBUFFERED
 If this is set to a non-empty string it is equivalent to specifying
 the \fB\-u\fP option.