Add installation instructions to the README

On copying the documentation from heroku I came accross installation instructions that seem to have gotten lost when the project came to github. I felt it would be useful to reintegrate them in the README. I don't know if there was a motivation for not bringing them in from heroku.
add uninstall instructions also

I'm not a veteran ruby expert, I don't know if this suffices.
Added ruby-dev to requirements in readme

For the gem install --dev option
Use rspec2 instead of legacy rspec

All tests pass, but with deprecated methods.
Deprecated function in rspec2: stub!

Replaced by stub
Deprecated methods in rspec2: mock

Replaced by double
All tests run cleanly
Merge branch 'master' into hotfix/readmeInstallInstructions

* master:
  Add development group to Gemfile
  Improve work with requirements. Remove circular dependency and some "require rubygems"
  Update website and meta in the readme
  Add documentation and .gem file to .gitignore
Merge branch 'hotfix/readmeInstallInstructions' into develop

* hotfix/readmeInstallInstructions:
  Added ruby-dev to requirements in readme
  add uninstall instructions also
  Add installation instructions to the README
Add .bundle to .gitignore

As per http://bundler.io/v1.3/rationale.htm this is automated configuration files which should not be under version control.
Update the bundle dependencies to include rspec 2

This update was done running bundle update to update all dependencies. All tests pass.

Gemfile.lock add's hard dependency versions to this gem. 
It was forcing rspec down to 1.2.6.

This reference (http://bundler.io/v1.3/rationale.html) seems to say that you should check it into versioning, but then it would be good to explain somewhere in development docs that you need to regenerate Gemfile.lock with 'bundle update' before pushing and that you should test if things work with bundle install. I just completely bypassed bundle causing this version conflict.

See also this, which seems to claim it's a bad idea to put Gemfile.lock in version control: 
http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/

A good explanation can also be found in "man bundle install", especially the section on deployment mode.
Try to work around travis bug travis-ci/travis-ci#2220

Not sure if it'll work but it's worth to try
Merge branch 'feature/rspec2' into develop

* feature/rspec2:
  Try to work around travis bug travis-ci/travis-ci#2220
  Update the bundle dependencies to include rspec 2
  Add .bundle to .gitignore