Added submodules, credentials, and profile information to README. Copied the sample credentials from marketplace-tests since it was much more informative.
Added more detailed information on running tests individually or in groups
Updates as per comments: removed extraneous info from credentials, added cloning info, updated instructions on running tests.
As per discussion on IRC, don't include specific information on running destructive tests. Include a line about how to get the options for running tests.
Merge pull request #36 from jessamynsmith/master

Added more info for new users