Updated config example in README

Changed external property in config example. The previous example used an array and led to issues creating invites on the first setup for newbies. The multiserver net plugin seems to call `replace()` on the external property, which does not work for arrays.

README.md

···
   "connections": {
     "incoming": {
       "net": [
-        { "scope": "public", "host": "0.0.0.0", "external": ["Your Host Name or Public IP"], "transform": "shs", "port": 8008 }
+        { "scope": "public", "host": "0.0.0.0", "external": "Your Host Name or Public IP", "transform": "shs", "port": 8008 }
       ]
     },
     "outgoing": {