Show count for the number of times this Product was sold

I think this does 'Number of units sold' on #6
Do not run subsequent commands on the readme if a previous command fails (could cause weird side effects)
Add missing unique indexes
Fix documentation for installing phantomjs
Specify that you need a heroku account (Heroku event)
Add performance testing/travis to README
Update readme
Add fork instructions
Fix typo in readme
Merge pull request #10 from mayokechu/master

Add conditionals to the README commands in case one of them fails (to prevent side effects)
Merge pull request #9 from ctshryock/products_show

Show count for the number of times this Product was sold