Update index.html

Updates the cheet sheet to display the abilities of the schema builder in being able to create dual indexes as per the api docs http://laravel.com/api/class-Illuminate.Database.Schema.Blueprint.html
Update index.html

Accidentally placed the comments below instead of above the lines that were being described
Update index.html

Makes it clear that the find and findOrFail functions on models will accept arrays of multiple columns if they're apart of a dual primary key. http://laravel.com/api/source-class-Illuminate.Database.Eloquent.Model.html#380-397
Merge pull request #46 from peterfox/master

Update index.html