Update Readme.md

Readme.md

@@ -139,17 +139,6 @@ Each top-level component receives a `url` property with the following API:
 - `pushTo(url)` - performs a `pushState` call that renders the new `url`. This is equivalent to following a `<Link>`
 - `replaceTo(url)` - performs a `replaceState` call that renders the new `url`
 
-### Error handling
-
-404 or 500 errors are handled both client and server side by a default component `error.js`. If you wish to override it, define a `_error.js`:
-
-```jsx
-import React from 'react'
-export default ({ statusCode }) => (
-  <p>An error { statusCode } occurred</p>
-)
-```
-
 ### Production deployment
 
 To deploy, run:
@@ -174,3 +163,10 @@ For example, to deploy with `now` a `package.json` like follows is recommended:
   }
 }
 ```
+
+### In progress
+
+- [ ] Add option to supply a `req`, `res` handling function for custom routing
+- [ ] Add option to supply a custom error component to render 404, 500 pages
+- [ ] Add option to extend or replace custom babel configuration
+- [ ] Add option to extend or replace custom webpack configuration