Add an example for repository access

[igorshapiro]

async findByName(name) {
    const repository = await Q.Models.User.repository
    const collection = repository.adapter.client.collection('users')
    return collection.find({ name }).toArray()
  }

[ondrej-kvasnovsky]

Because what I need, is mongo collection, I just injected mongo into my class, something like this.

module.exports = class {
  constructor(mongo) {
    this.mongo = mongo
  }

  async userCollection() {
    return this.mongo.collection('user')
  }
}```

I think this is more clear, better than through Q.Models