Comment guest access initial state

src/components/structures/MatrixChat.js

@@ -382,6 +382,9 @@ module.exports = React.createClass({
 
                 MatrixClientPeg.get().createRoom({
                     preset: "private_chat",
+                    // Allow guests by default since the room is private and they'd
+                    // need an invite. This means clicking on a 3pid invite email can
+                    // actually drop you right in to a chat.
                     initial_state: [
                         {
                             content: {