[Buildbot] #2929: document BuildStep renderables variable

[Buildbot trac]

#2929: document BuildStep renderables variable
-------------------------+--------------------
Reporter:  vlovich       |       Owner:
    Type:  task          |      Status:  new
Priority:  major         |   Milestone:  0.9.+
 Version:  0.8.9         |  Resolution:
Keywords:  docs, simple  |
-------------------------+--------------------
Changes (by dustin):

 * keywords:   => docs, simple
 * milestone:  undecided => 0.9.+


Comment:

 Good idea

--
Ticket URL: <http://trac.buildbot.net/ticket/2929#comment:1>
Buildbot <http://buildbot.net/>
Buildbot: build/test automation