Add Inspecting The Process Message Queue as an elixir til

elixir/inspecting-the-process-message-queue.md

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+# Inspecting The Process Message Queue
+
+A core tenant of Elixir is message passing between processes. So, if a
+process is sent a message, where does that message go? What happens if it
+gets sent many messages? The `Process.info/2` function allows us to inspect
+the message queue.
+
+First, let's send some messages (to ourself) and then keep an eye on the
+length of the message queue as we go.
+
+```elixir
+> send self(), {:error, "this is bad"}
+{:error, "this is bad"}
+> Process.info(self(), :message_queue_len)
+{:message_queue_len, 1}
+> send self(), {:hello, "world"}
+{:hello, "world"}
+> Process.info(self(), :message_queue_len)
+{:message_queue_len, 2}
+```
+
+Now, I am curious what those specific messages are. Let's ask
+`Process.info/2` for the messages that are in the message queue.
+
+```
+> Process.info(self(), :messages)
+{:messages, [error: "this is bad", hello: "world"]}
+```
+
+There are a lot of other things that `Process.info/2` can tell us about a
+process. See [the Erlang docs for
+`process_info`](http://erlang.org/doc/man/erlang.html#process_info-2) for
+more details.