docs: netdev: add a cheat sheet for the rules

Summarize the rules we see broken most often and which may
be less familiar to kernel devs who are used to working outside
of netdev.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: kuba-moo

Documentation/process/maintainer-netdev.rst

@@ -6,6 +6,15 @@
 netdev FAQ
 ==========
 
+tl;dr
+-----
+
+ - designate your patch to a tree - ``[PATCH net]`` or ``[PATCH net-next]``
+ - for fixes the ``Fixes:`` tag is required, regardless of the tree
+ - don't post large series (> 15 patches), break them up
+ - don't repost your patches within one 24h period
+ - reverse xmas tree
+
 What is netdev?
 ---------------
 It is a mailing list for all network-related Linux stuff.  This