[ruby/dbm] gemspec: add README & LICENSE

ruby/dbm@c86b94b781

Author: olleolleolle

ext/dbm/dbm.gemspec

@@ -6,7 +6,7 @@ Gem::Specification.new do |s|
   s.description = "Provides a wrapper for the UNIX-style Database Manager Library"
 
   s.require_path = %w{lib}
-  s.files = %w{ext/dbm/extconf.rb ext/dbm/dbm.c}
+  s.files = %w{README.md LICENSE.txt ext/dbm/extconf.rb ext/dbm/dbm.c}
   s.extensions = %w{ext/dbm/extconf.rb}
   s.required_ruby_version = ">= 2.3.0"