README for Firebase example

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Update README.md

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Rename folder for Firebase sample

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Create AWS sample project.
Login with Lock
Fetch AWS credentials with delegation API.
Download file from S3 using delegation creds.
Merge pull request #51 from auth0/chore-aws-sample

AWS Sample
Remove unnecesary constraints.
Username validator.
Email validator.
Password validation (non empty).
Confirm password validation.
Credentials validator.
More tests.
Use new validators in Sign Up.
Use new validators in auth screens.

Remove old validators.