Update README file after integrating stryker

[enriquezrene]

As part of the stryker integration, a new change has been introduced in the project. Now the existing file.keys.json is no longer needed, and a new file keys.ts should be created with the following constants:

export const AUTHORITY = 'XXX';
export const CLIENT_ID = 'XXX';
export const SCOPES = ['XXX'];

Values should not be hardcoded and they are available in the slack channel.