Fixes #965: Clarify PHP version support in README.

README.md

@@ -26,7 +26,9 @@
 | [main](https://github.com/consolidation/robo)      | 4 only    | [![PHP 7 only](https://img.shields.io/badge/PHP%207-only-92a9ed)](https://travis-ci.org/consolidation/Robo) |
 | [1.x](https://github.com/consolidation/robotree/1.x) | 2, 3 or 4 | [![PHP 5 supported](https://img.shields.io/badge/PHP%205-supported-408677)](https://travis-ci.org/consolidation/Robo) |
 
-Robo versions 2.x and 1.x are largely compatible; however, Robo 2.x supports fewer versions of PHP and Symfony. This is to make ongoing maintenance easier; Robo 1.x will be supported less and less over time. Projects should update to Robo ^2 if possible.
+The pre-build [robo.phar](http://robo.li/robo.phar) is built with Symfony 5, and requires PHP 7.2+.  Robo also works with Symfony 4 and PHP 7.1.3+ if packaged as a library in another application.
+
+For Symfony 2 or 3 support, or PHP versions prior to 7.1, please use the Robo 1.x branch.
 
 ## Installing