Update genserver.markdown

Author: josevalim

getting-started/mix-otp/genserver.markdown

@@ -238,17 +238,17 @@ Finally, different from the other callbacks, we have defined a "catch-all" claus
 
 ## `call`, `cast` or `info`?
 
-So far we have used three callbacks: `handle_call/3`, `handle_cast/2` and `handle_info/2`. Deciding when to use each is straightforward:
+So far we have used three callbacks: `handle_call/3`, `handle_cast/2` and `handle_info/2`. Here is what we should consider when deciding when to use each:
 
 1. `handle_call/3` must be used for synchronous requests. This should be the default choice as waiting for the server reply is a useful backpressure mechanism.
 
 2. `handle_cast/2` must be used for asynchronous requests, when you don't care about a reply. A cast does not even guarantee the server has received the message and, for this reason, must be used sparingly. For example, the `create/2` function we have defined in this chapter should have used `call/2`. We have used `cast/2` for didactic purposes.
 
-3. `handle_info/2` must be used for all other messages a server may receive that are not sent via `GenServer.call/2` or `GenServer.cast/2`, including regular messages sent with `send/2`. The monitoring `:DOWN` messages are a perfect example of this.
+3. `handle_info/2` must be used for all other messages a server may receive that are not sent via `GenServer.call/2` or `GenServer.cast/2`, including regular messages sent with `send/2`. The monitoring `:DOWN` messages are such an example of this.
 
-Since any message, including the ones sent via `send/2`, go to `handle_info/2`, there is a chance unexpected messages will arrive to the server. Therefore, if we don't define the catch-all clause, those messages could lead our registry to crash, because no clause would match.
+Since any message, including the ones sent via `send/2`, go to `handle_info/2`, there is a chance unexpected messages will arrive to the server. Therefore, if we don't define the catch-all clause, those messages could lead our registry to crash, because no clause would match. We don't need to worry about such cases for `handle_call/3` and `handle_cast/2` though. Calls and casts are only done via the `GenServer` API, so an unknown message is quite likely to be due to a developer mistake.
 
-We don't need to worry about this for `handle_call/3` and `handle_cast/2` because these requests are only done via the `GenServer` API, so an unknown message is quite likely to be due to a developer mistake.
+To help developers remember the differences between call, cast and info, their valid return types and more, [Benjamin Tan Wei Hao](http://benjamintan.io) has created a [GenServer cheat sheet](https://raw.githubusercontent.com/benjamintanweihao/elixir-cheatsheets/master/GenServer_CheatSheet.pdf). The cheat sheet can also be found as part of [The Little Elixir and OTP Guidebook](https://www.manning.com/books/the-little-elixir-and-otp-guidebook).
 
 ## Monitors or links?
 
@@ -265,6 +265,3 @@ ref = Process.monitor(pid)
 
 This is a bad idea, as we don't want the registry to crash when a bucket crashes! We typically avoid creating new processes directly, instead we delegate this responsibility to supervisors. As we'll see in the next chapter, supervisors rely on links and that explains why link-based APIs (`spawn_link`, `start_link`, etc) are so prevalent in Elixir and <abbr title="Open Telecom Platform">OTP</abbr>.
 
-## Having trouble remembering everything?
-
-You don't have to! [Benjamin Tan Wei Hao](http://benjamintan.io), author of [The Little Elixir and OTP Guidebook](https://www.manning.com/books/the-little-elixir-and-otp-guidebook), has created a [GenServer cheat sheet](https://raw.githubusercontent.com/benjamintanweihao/elixir-cheatsheets/master/GenServer_CheatSheet.pdf) that captures the essential steps needed to quickly get started with using GenServer. Get it [here](https://raw.githubusercontent.com/benjamintanweihao/elixir-cheatsheets/master/GenServer_CheatSheet.pdf).