Document PYTHONDEVMODE in the manpage

Author: stefanor

Misc/python.man

@@ -577,6 +577,12 @@ allocator of the C library, or if Python is configured without pymalloc support.
 If set to the value 0, causes the main Python command line application to skip
 coercing the legacy ASCII-based C and POSIX locales to a more capable UTF-8
 based alternative.
+.IP PYTHONDEVMODE
+If this environment variable is set to a non-empty string, enable Python's
+"development mode", introducing additional runtime checks that are too
+expensive to be enabled by default.
+.IP
+This is equivalent to the \fB\-X dev\fR option.
 .IP PYTHONASYNCIODEBUG
 If this environment variable is set to a non-empty string, enable the debug
 mode of the asyncio module.