add React Day Berlin to supporters

Author: robhrt7

data/supporters.json

@@ -1357,6 +1357,18 @@
           "email": "[email protected]"
         }
       ]
+    },
+    {
+      "name": "React Day Berlin",
+      "city": "Berlin",
+      "country": "Germany",
+      "link": "https://reactday.berlin",
+      "contacts": [
+        {
+          "name": "Robert Haritonov",
+          "twitter": "operatino"
+        }
+      ]
     }
   ]
 }