docs: add channel_name cookie docs

Author: Ziinc

README.md

@@ -37,11 +37,13 @@ config :libcluster,
           database: "postgres",
           port: 5432,
           parameters: [],
+          # optional, defaults to node cookie
           channel_name: "cluster"
       ],
     ]
   ]
 ```
+
 Then add it to your supervision tree:
 
 ```elixir
@@ -60,6 +62,6 @@ defmodule MyApp do
 end
 ```
 
-
 ## Acknowledgements
-A special thank you to [@gotbones](https://twitter.com/gotbones) for creating libcluster and [@kevinbuch_](https://twitter.com/kevinbuch_) for the original inspiration for this strategy.
+
+A special thank you to [@gotbones](https://twitter.com/gotbones) for creating libcluster and [@kevinbuch\_](https://twitter.com/kevinbuch_) for the original inspiration for this strategy.

lib/strategy.ex

@@ -11,7 +11,7 @@ defmodule LibclusterPostgres.Strategy do
   ## Options
 
   * `heartbeat_interval` - The interval at which to send heartbeat messages in milliseconds (optional; default: 5_000)
-  * `channel_name` - The name of the channel to which nodes will listen and notify (optional; default: "cluster")
+  * `channel_name` - The name of the channel to which nodes will listen and notify (optional; defaults to the result of `Node.get_cookie/0`)
   """
   use GenServer