Merge pull request #151 from artsy/expand-render-prop-doc

[README] Expand render-prop doc

README.md

@@ -398,18 +398,19 @@ The examples given for each prop use breakpoint definitions as defined in the
 above ‘Setup’ section.
 
 If you would like to avoid the underlying div that is generated by `<Media>` and
-instead use your own element, use the render-props form:
+instead use your own element, use the render-props form but be sure to **not**
+render any children when not necessary:
 
 ```tsx
 export const HomePage = () => {
   return (
     <>
       <Media at="sm">Hello mobile!</Media>
       <Media greaterThan="sm">
-        {(mediaClassNames) => {
+        {(mediaClassNames, renderChildren) => {
           return (
             <MySpecialComponent className={mediaClassNames}>
-              Hello desktop!
+              {renderChildren ? "Hello desktop!" : null}
             </MySpecialComponent>
           )
         }}