Add redux-optimist and group it with redux-undo

Author: gaearon

docs/introduction/Ecosystem.md

@@ -29,14 +29,18 @@ On this page we will only feature a few of them that the Redux maintainers have
 * [redux-batched-subscribe](https://github.com/tappleby/redux-batched-subscribe) — Customize batching and debouncing calls to the store subscribers
 * [redux-history-transitions](https://github.com/johanneslumpe/redux-history-transitions) — History transitions based on arbitrary actions
 
+## Reducer Enhancers
+
+* [redux-optimist](https://github.com/ForbesLindesay/redux-optimist) — Optimistically apply actions that can be later commited or reverted
+* [redux-undo](https://github.com/omnidan/redux-undo) — Effortless undo/redo and action history for your reducers
+
 ## Utilities
 
 * [reselect](https://github.com/faassen/reselect) — Efficient derived data selectors inspired by NuclearJS
 * [normalizr](https://github.com/gaearon/normalizr) — Normalize nested API responses for easier consumption by the reducers
 * [redux-actions](https://github.com/acdlite/redux-actions) — Reduces the boilerplate in writing reducers and action creators
 * [redux-transducers](https://github.com/acdlite/redux-transducers) — Transducer utilities for Redux
 * [redux-immutablejs](https://github.com/indexiatech/redux-immutablejs) — Integration tools between Redux and [Immutable](https://github.com/facebook/immutable-js/)
-* [redux-undo](https://github.com/omnidan/redux-undo) — Effortless undo/redo and action history for your reducers
 * [redux-tcomb](https://github.com/gcanti/redux-tcomb) — Immutable and type-checked state and actions for Redux
 
 ## Developer Tools