add -3 to manpage

Misc/python.man

@@ -54,6 +54,9 @@ python \- an interpreted, interactive, object-oriented programming language
 [
 .B \-x
 ]
+[
+.B \-3
+]
 .br
        [
 .B \-c
@@ -236,6 +239,9 @@ is thus equivalent to an omitted line number.
 Skip the first line of the source.  This is intended for a DOS
 specific hack only.  Warning: the line numbers in error messages will
 be off by one!
+.TP
+.B \-3
+Warn about Python 3.x incompatibilities that 2to3 cannot trivially fix.
 .SH INTERPRETER INTERFACE
 The interpreter interface resembles that of the UNIX shell: when
 called with standard input connected to a tty device, it prompts for