Update CLA information to reflect EasyCLA
This is a minor change to update the CLA instructions.
## Contributor License Agreement ("CLA")
-In order to accept your pull request, we need you to submit a CLA. You only need to do this once, so if you've done this for another Facebook open source project, you're good to go. If you are submitting a pull request for the first time, just let us know that you have completed the CLA and we can cross-check with your GitHub username.
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-Complete your CLA here: <https://code.facebook.com/cla>
+In order to accept your pull request, we need you to submit a CLA. You only need to do this once, so if you've done this for one repository in the [prestodb](https://github.com/prestodb) organization, you're good to go. If you are submitting a pull request for the first time, the communitybridge-easycla bot will notify you if you haven't signed, and will provide you with a link. If you are contributing on behalf of a company, you might want to let the person with manages your corporate CLA whitelist know they will be receiving a request from you.
## License
