Add documentation to port directive.

Author: ioquatix

guides/deployment/readme.md

@@ -103,9 +103,10 @@ service hostname do
 
 	# If using count > 1 you may want to preload your app to reduce memory usage and increase performance:
 	preload "preload.rb"
-
+	
+	# The default port should be 3000, but you can change it to match your Heroku configuration.
 	port {ENV.fetch("PORT", 3000).to_i}
-
+	
 	# Heroku only supports HTTP/1.1 at the time of this writing. Review the following for possible updates in the future:
 	# https://devcenter.heroku.com/articles/http-routing#http-versions-supported
 	# https://github.com/heroku/roadmap/issues/34