[Enhancement] Allow IPv6 (#372)

* Added option to enable IPv6 in runtime config

* Updated README

config/runtime.exs

@@ -66,6 +66,7 @@ if config_env() == :prod do
   journal_mode = String.to_existing_atom(System.get_env("JOURNAL_MODE", "wal"))
   # For running PF in a subdirectory via a reverse proxy
   base_route_path = System.get_env("BASE_ROUTE_PATH", "/")
+  enable_ipv6 = String.length(System.get_env("ENABLE_IPV6", "")) > 0
 
   config :logger, level: String.to_existing_atom(System.get_env("LOG_LEVEL", "debug"))
 
@@ -120,7 +121,7 @@ if config_env() == :prod do
       # Set it to  {0, 0, 0, 0, 0, 0, 0, 1} for local network only access.
       # See the documentation on https://hexdocs.pm/plug_cowboy/Plug.Cowboy.html
       # for details about using IPv6 vs IPv4 and loopback vs public addresses.
-      ip: {0, 0, 0, 0},
+      ip: if(enable_ipv6, do: {0, 0, 0, 0}, else: {0, 0, 0, 0, 0, 0, 0, 0}),
       port: String.to_integer(System.get_env("PORT") || "4000")
     ],
     url: [path: base_route_path],