[PATCH] Mention python versions in README.Coding

[Andrew Bartlett]

On Fri, 2018-03-23 at 15:24 +1300, Douglas Bagnall via samba-technical
wrote:
> Being compatible across versions 2.6 - 3.6 is an important thing for
> Python contributors to think about, so we should mention it.
> 
> Also remove a reference to prog_guide4.txt, which disappeared a few
> weeks ago.

This is great, thanks.

Reviewed-by: Andrew Bartlett <abartlet at samba.org>

Please push when ready.

Andrew Bartlett

-- 
Andrew Bartlett
https://samba.org/~abartlet/
Authentication Developer, Samba Team         https://samba.org
Samba Development and Support, Catalyst IT   
https://catalyst.net.nz/services/samba