top.md doesn't provide state files for users without the Vagrant environment

[stooj]

If you follow the tutorial but choose not to use the Vagrant demo environment, applying the final top.sls results in an error.

salt '*' state.apply

minion1:
    Data failed to compile:
----------
    No matching sls found for 'common' in env 'base'
minion2:
    Data failed to compile:
----------
    No matching sls found for 'common' in env 'base'

Instructions to create the common directory could be added, along with instructions to populate it with something suitable.

[goetzk]

I also noticed that error but assumed it was something i had done. I'd be happy to submit a patch adding a common file with some arbitrary contents if that would be of assistance.