Setup Instructions missing permissions

[pklapperich]

This app requires the "Read-only access to Emails" permission, yet the README.md does not mention this. I recommend the following:

Setup
-----

Create a new application under your organization in GitHub. Enter the **Authorization
callback URL** as the prefix to your Sentry installation:

::

    https://example.sentry.com

Configure the application with Read-Only permissions for:

::

    Emails: Manage a user's email.