Update README.md with event handling descriptions #260

README.md

@@ -868,6 +868,8 @@ on the `messages` table and selecting "properties":
 
 ![pgadmin-messages-schema-columns-view](https://user-images.githubusercontent.com/194400/35623295-c3a4df5c-0693-11e8-8484-199c2bcab458.png)
 
+> _**Note**: For sections 7, 8, and 9 we will be fleshing out how our code "handles" the different events that can occur in our chat app. Phoenix abstracts away much of the underlying message-passing logic in Elixir's process communication (for more info on how Elixir processes communicate, read [here](https://hexdocs.pm/elixir/processes.html)). In Phoenix, events/messages sent from the client are automatically routed to the corresponding handler functions based on the event name, making message handling seamless and straightforward!._
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 ## 7. Insert Messages into Database
@@ -888,6 +890,8 @@ def handle_in("shout", payload, socket) do
 end
 ```
 
+If you noticed earlier, in our `assets/js/app.js` file, we used the function `sendMessage()` to *push* our message to the server on the "shout" event. Phoenix routes the message to the server-side `handle_in("shout", payload, socket)` function because the event name matches 'shout'. In this function, we handle the payload (which is the message text and any other data) and insert it into our database. Neat!
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@@ -951,6 +955,8 @@ def join("room:lobby", payload, socket) do
 end
 ```
 
+> _**Note**: like section 7, Phoenix knows to call this function when the server sends the internal message `:after_join` via the channel process. Our `join/3` function in `lib/chat_web/channels/room_channel.ex` sends that `:after_join message` to the channel process when the client successfully connects to the `"room:lobby"` topic._
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