Add composer.json template in preparation for the new plugin repository

composer.json-dist

@@ -0,0 +1,16 @@
+{
+    "name": "roundcube/roundcubemail",
+    "description": "The Roundcube Webmail suite",
+    "license": "GPL-3.0+",
+    "repositories": [
+        {
+            "type": "composer",
+            "url": "http://plugins.roundcube.net/"
+        }
+    ],
+    "require": {
+        "php": ">=5.3.0",
+        "roundcube/plugin-installer": ">=0.1.3"
+    },
+    "minimum-stability": "dev"
+}