docs: add channel_name cookie docs

Author: Ziinc

README.md

@@ -4,7 +4,6 @@ Postgres Strategy for [libcluster](https://hexdocs.pm/libcluster/) which is used
 
 It uses Postgres `LISTEN` and `NOTIFICATION` to send the information from a given node and connects them using libcluster.
 
-
 ```elixir
 config :libcluster,
   topologies: [
@@ -17,6 +16,7 @@ config :libcluster,
           database: "postgres",
           port: 5432,
           parameters: [],
+          # optional, defaults to node cookie
           channel_name: "cluster"
       ],
     ]
@@ -25,7 +25,6 @@ config :libcluster,
 
 To see it in use run the script `./test.sh` in this folder and you will see that both nodes connected as expected and are able to list one another.
 
-
 ## Installation
 
 The package can be installed

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