Update to econsensus README file

[Jo Paulger]

Hi all,

I've just made some small changes to the README file for the econsensus project to clarify the desired workflow for contributors in general, and in particular to emphasize the use of the 'develop' rather than the 'master' branch as a baseline to start working on. I've also ensured that those changes appear in both the master and develop branches, so no matter which branch you're looking at on github, you see those notes :D

Thanks,

Jo