Readme: Incubator and branding.

[Patrick Hunt <ph...@apache.org>]

Hi folks. Please make sure you read and understand the branding guidelines
http://incubator.apache.org/guides/branding.html
there are additional limitations for podlings over a regular Apache
TLP that need to be followed.

In particular if you work for a company that would like to, for
example, release a press release about the project at any stage during
incubation you need to work with Apache branding team. (more about
that on the linked page).

Patrick