Clarify master config yaml format

[stefanseefeld]

Setting up a demo buildbot-travis instance on a dedicated machine, then accessing the web interface from another machine, results in the error / warning

Warning: c['buildbotURL'] is misconfigured to
http://localhost:8010/
Should be:
http://buildbot:8010/

grepping through all the config files to identify the faulty setting only yields master.cfg.sample. The real master.cfg file uses the TravisConfigurator to read the config in from cfg.yml, but that neither contains a buildbotURL nor do I find any documentation for where to add it.

[levitte]

The only solution I found was to add this line in the generated master.cfg:

c['buildbotURL'] = "https://buildbot:8010/"