Add missing step in usage (#117)

Author: sweoggy

README.md

@@ -18,6 +18,7 @@ If you don't use Symfony Flex:
 
 ## Usage
 
+- require the RoadRunner download utility: `composer require --dev spiral/roadrunner-cli`
 - get the RoadRunner binary: `vendor/bin/rr get --location bin/`
 - run RoadRunner with `bin/rr serve` or `bin/rr serve -c .rr.dev.yaml` (watch mode)
 - visit your app at http://localhost:8080

composer.json

@@ -34,6 +34,7 @@
     },
     "suggest": {
         "nyholm/psr7": "For a super lightweight PSR-7/17 implementation",
+        "spiral/roadrunner-cli": "For easy installation of RoadRunner",
         "symfony/proxy-manager-bridge": "For doctrine re-connection implementation"
     },
     "require-dev": {