[Buildbot] #2989: Improve a bit documentation for Docker

[Buildbot trac]

#2989: Improve a bit documentation for Docker
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Reporter:  sa2ajj        |       Owner:  dustin
    Type:  enhancement   |      Status:  assigned
Priority:  major         |   Milestone:  0.9.0
 Version:  master        |  Resolution:
Keywords:  docs, docker  |
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Comment (by dustin):

 That works!

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Ticket URL: <http://trac.buildbot.net/ticket/2989#comment:7>
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