docs: section link Error Handling (postcss#293)

Author: guspan-tanadi

API.md

@@ -786,7 +786,7 @@ has a method `error(message, options)` that returns an
 error object. This method should always be used to raise
 errors relating to the syntax of selectors. The options
 to this method are passed to postcss's error constructor
-([documentation](http://api.postcss.org/Container.html#error)).
+([documentation](http://postcss.org/api/#container-error)).
 
 #### Async Error Example