Makes a few updates to the required files and updates the README with instructions and pointers on how to work on the gem

Changes to teamsnap_rb.rb were necessary to work with the gem in `irb`.
README updates reflect what I've found to be a decent workflow when working on the gem.
This was actually necessary to add because conglomerate doesn't explicitly require forwardable, but it uses it. Perhaps this should be added to conglomerate instead?