Enhancement: Add link to source to composer.json

Author: localheinz

Diff for: composer.json

@@ -10,6 +10,9 @@
             "homepage": "https://www.php-fig.org/"
         }
     ],
+    "support": {
+        "source": "https://github.com/php-fig/event-dispatcher"
+    },
     "require": {
         "php": ">=7.2.0"
     },