READE.md need update

[elycheikhsmail]

I think example in README.md need be update for those raisons :

• by default db must be sqlite3 for easy copy-past test and learning
• connexion to other pg/mysql example can be mention but commented
• fix the bug const sfFlight = await Flight.select('destination').find(2); must be sfFlight = await Flight.select('id', 'destination').find(2); otherwise await sfFlight.delete(); will faild because don't have id