Update README.md

README.md

@@ -11,6 +11,7 @@ Automatically generate your API documentation from your existing Laravel routes.
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+> Note: this is the documentation for version 3, which changes significantly from version 2. if you're on v2, you can check out its documentation [here](https://github.com/mpociot/laravel-apidoc-generator/blob/2.x/README.md). We strongly recommend you upgrade, though, as v3 is more robust and fixes a lot of the problems with v2.
 
 ## Installation
 > Note: version 3.x requires PHP 7 and Laravel 5.5 or higher. Version 2.x requires Laravel 5.4.