Add a list of alternatives

Author: matthew-andrews

README.md

@@ -50,3 +50,8 @@ fetch('//offline-news-api.herokuapp.com/stories')
 ## License
 
 All open source code released by FT Labs is licenced under the MIT licence.  Based on [the fine work by](https://github.com/github/fetch/pull/31) **[jxck](https://github.com/Jxck)**.
+
+## Alternatives
+
+- [cross-fetch](https://github.com/lquixada/cross-fetch#why-not-isomorphic-fetch)
+- Using [node-fetch](https://github.com/node-fetch/node-fetch) and the [Fetch polyfill](https://github.com/github/fetch) directly (or from [polyfill.io](https://polyfill.io), or relying on [the browser's implementation of the Fetch API](https://caniuse.com/fetch)).