* lib/securerandom.rb: [DOC] Add note on require for examples
  Based on a patch by @schneems [Fixes GH-518] [ci skip]
  https://github.com/ruby/ruby/pull/518


git-svn-id: svn+ssh://svn.ruby-lang.org/ruby/trunk@44782 b2dd03c8-39d4-4d8f-98ff-823fe69b080e