Add notes about composing multiple contexts

content/docs/context.md

@@ -91,8 +91,12 @@ A more complex example with dynamic values for the theme:
 
 ## Consuming Multiple Contexts
 
+To keep context re-rendering fast, React needs to make each context consumer a separate node in the tree. 
+
 `embed:context/multiple-contexts.js`
 
+If two or more context values are often used together, you might want to consider creating your own render prop component that provides both. [React Context Composer](https://github.com/FormidableLabs/react-context-composer/) is a simple library to help with this.
+
 ## Accessing Context in Lifecycle Methods
 
 `embed:context/lifecycles.js`