Add Tickets handling entry to Contributing

Looking for some feedback on the content before updating the labels in CocoaPods. I created this as a resource for future bug bags and to improve our efficiency in handling tickets. As always edits, directly committing, to this branch are welcome.

Needs englishification.

@CocoaPods/owners 
@CocoaPods/push 

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The contributing section is becoming and will become crowded.

It would be also nice to display the following in 4 columns... opinions?

![screen shot 2014-04-02 at 11 04 15](https://cloud.githubusercontent.com/assets/1048705/2589038/224f6462-ba46-11e3-9966-e36cc376dc3b.png)