Update subscribe.ms
Update subscribe.ms

In `subscribeToNewComments` documentation, the suggestion usage is in the `componentWillMount` lifecycle.

According to the [react documentation](https://reactjs.org/docs/react-component.html#componentwillmount) about it, it's better to avoid using subscription, and rely on `componentDidMount` instead.

[Twitter reply](https://twitter.com/apollographql/status/968693661608415233) for reference.
apollostack/apollo-client,apollographql/apollo-client,apollostack/apollo-client,apollostack/apollo-client,apollographql/apollo-client