docs(README): Fix example for subscribe and subscribeToMore methods

[Tobino]

Add 2 examples for both subscribe and subscribeToMore.

subscribeToMore is not a function on apolloClient but working on a query result. Fix #265
subscribe need a subscriber for a full working example.

Both example were test with hybrid and Full WebSocket Transport.

TODO:

• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass
• Update CHANGELOG.md with your change

[mistic]

The api on the examples won't work with apollo-client 2.X version, however I think we can still merge it for the time being.

@NeoPhi @DxCx @dotansimha @Urigo can u give your thoughts here please?