Improve testing notes?

Hackers:

I've added the following section to "how to beta test":

https://wiki.postgresql.org/wiki/HowToBetaTest#Particular_Things_to_Test_in_9.5

It would be great if other folks could add particular things they'd like
to see users test, so that we can make the alpha/beta cycle as fast and
fruitful as possible.

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com