Edit custom error hundling readme (#5571)

* add description of importing _error.js

* fix description of importing _error.js

* delete .idea folder

packages/next/README.md

@@ -1185,7 +1185,7 @@ export default class Page extends React.Component {
 }
 ```
 
-> If you have created a custom error page you have to import your own `_error` component instead of `next/error`
+> If you have created a custom error page you have to import your own `_error` component from `./_error` instead of `next/error`
 
 ### Custom configuration