Add links to example apps in readme

[Webb Hinton]

It'd be great if the readme included some links to some non-trivial demo apps that use easy peasy. While the docs do a good job of providing examples for most of the APIs, having some more real world examples would help users learn more advanced patterns and integrations.

Here's one, for example:
https://github.com/crissdev/reduxtagram-easy-peasy
I know https://github.com/wbkd/react-flow also uses easy peasy for state management.