bin/mdcat in mdcat-0.3.0 vs bin/mdcat in mdcat-0.4.0

@@ -4,10 +4,12 @@
 $LOAD_PATH.unshift(File.expand_path("../lib", __dir__))
 
 require "mdcat"
 require "tty-markdown"
 
+DEFAULT_FILES = %w[README.md index.md].freeze
+
 BANNER = %q(
           _         _
  _ __  __| |__ __ _| |_
 | '  \/ _` / _/ _` |  _|
 |_|_|_\__,_\__\__,_|\__|
@@ -35,10 +37,12 @@
   help
   exit(0)
 end
 
 # validations
-file_path = ARGV[0]
+file_path =
+  ARGV[0] || DEFAULT_FILES.find { |file| File.exist?(file) }
+
 if file_path.nil?
   help
   exit(1)
 end