fix README typo (vercel#4476)

`idead` to `idea`

Author: dlcoffee

examples/with-zones/README.md

@@ -31,7 +31,7 @@ npm install
 yarn
 ```
 
-## The idead behind this example
+## The idea behind this example
 
 With Next.js you can use multiple apps as a single app using it's multi-zones feature.
 This is an example showing how to use it.