[Buildbot] #2945: Add an example of using codebases

[Buildbot trac]

#2945: Add an example of using codebases
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Reporter:  sa2ajj            |       Owner:  Ben
    Type:  enhancement       |      Status:  assigned
Priority:  patches-accepted  |   Milestone:  0.9.+
 Version:  master            |  Resolution:
Keywords:  docs              |
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Changes (by Ben):

 * owner:   => Ben
 * status:  new => assigned


Comment:

 It's been suggested on IRC to add a picture about the conversion from
 changes to sourcestamps to buildset in the introduction chapter. I'll give
 it a shot.

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Ticket URL: <http://trac.buildbot.net/ticket/2945#comment:2>
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