add preact-render-to-json (preactjs#726)

Author: nathancahill

README.md

@@ -90,6 +90,7 @@ Preact supports modern browsers and IE9+:
 
 - :raised_hands: [**preact-compat**](https://git.io/preact-compat): use any React library with Preact *([full example](http://git.io/preact-compat-example))*
 - :page_facing_up: [**preact-render-to-string**](https://git.io/preact-render-to-string): Universal rendering.
+- :loop: [**preact-render-to-json**](https://git.io/preact-render-to-json): Render for Jest Snapshot testing.
 - :earth_americas: [**preact-router**](https://git.io/preact-router): URL routing for your components
 - :bookmark_tabs: [**preact-markup**](https://git.io/preact-markup): Render HTML & Custom Elements as JSX & Components
 - :satellite: [**preact-portal**](https://git.io/preact-portal): Render Preact components into (a) SPACE :milky_way: