Clarify Rails::Generators::Actions#lib doc [ci-skip]

This makes it clear that, when using the block form, the file contents
is the return value of the block, rather than the code of the block.

(cherry picked from commit e58a9b0)

Author: jonathanhefner

railties/lib/rails/generators/actions.rb

@@ -261,14 +261,17 @@ def vendor(filename, data = nil)
         create_file("vendor/#{filename}", optimize_indentation(data), verbose: false)
       end
 
-      # Create a new file in the <tt>lib/</tt> directory. Code can be specified
-      # in a block or a data string can be given.
+      # Creates a file in +lib/+. The contents can be specified as an argument
+      # or as the return value of the block.
       #
-      #   lib("crypto.rb") do
-      #     "crypted_special_value = '#{rand}--#{Time.now}--#{rand(1337)}--'"
+      #   lib "foreign.rb", <<~RUBY
+      #     # Foreign code is fun
+      #   RUBY
+      #
+      #   lib "foreign.rb" do
+      #     "# Foreign code is fun"
       #   end
       #
-      #   lib("foreign.rb", "# Foreign code is fun")
       def lib(filename, data = nil)
         log :lib, filename
         data ||= yield if block_given?