Add gem descriptions and URLs to Gemfile.

Gemfile

@@ -6,11 +6,60 @@ source "http://rubygems.org"
 # Add dependencies to develop your gem here.
 # Include everything needed to run rake, tests, features, etc.
 group :development, :test do
+  # allocation_stats
+  #
+  # Tooling for tracing object allocations in Ruby 2.1
+  #
+  # https://rubygems.org/gems/allocation_stats/
+  # https://github.com/srawlins/allocation_stats
   gem "allocation_stats"
+  # minitest
+  #
+  # minitest provides a complete suite of testing facilities supporting TDD,
+  # BDD, mocking, and benchmarking.
+  #
+  # https://rubygems.org/gems/minitest
+  # https://github.com/seattlerb/minitest
   gem "minitest"
+  # mocha
+  #
+  # Mocking and stubbing library with JMock/SchMock syntax, which allows
+  # mocking and stubbing of methods on real (non-mock) classes.
+  #
+  # https://rubygems.org/gems/mocha
+  # http://gofreerange.com/mocha/docs/
+  # https://github.com/freerange/mocha
   gem "mocha"
+  # rake
+  #
+  # Rake is a Make-like program implemented in Ruby.
+  #
+  # https://rubygems.org/gems/rake
+  # https://github.com/ruby/rake
   gem "rake"
+  # rdoc
+  #
+  # RDoc produces HTML and command-line documentation for Ruby projects.
+  #
+  # https://rubygems.org/gems/rdoc
+  # http://docs.seattlerb.org/rdoc/
+  # https://github.com/rdoc/rdoc
   gem "rdoc"
+  # rubocop
+  #
+  # Automatic Ruby code style checking tool. Aims to enforce the
+  # community-driven Ruby Style Guide.
+  #
+  # https://rubygems.org/gems/rubocop
+  # https://github.com/bbatsov/rubocop
   gem "rubocop"
+  # test-unit
+  #
+  # Test::Unit (test-unit) is unit testing framework for Ruby, based on xUnit
+  # principles.
+  #
+  # https://rubygems.org/gems/test-unit
+  # http://test-unit.github.io/
+  # https://github.com/test-unit/
   gem "test-unit"
 end