Update documentation

In Readme we have:
```Go
 err := orm.Initialize(orm.ConnectionConfig{
    Driver:           "sqlite3",
    ConnectionString: ":memory:",
    DatabaseValidations: true,
  })
```

But this is the new way
```Go
err := orm.SetupConnections(orm.ConnectionConfig{
    DB: ,
    DatabaseValidations: true, 
})
```