Added comments to ruby code generation

examples/ruby/lib/helloworld_services.rb

examples/ruby/lib/route_guide_services.rb

src/compiler/ruby_generator.cc

src/compiler/ruby_generator_helpers-inl.h

src/ruby/bin/math_services.rb

src/ruby/pb/grpc/health/v1/health_services.rb

...ruby/pb/grpc/testing/duplicate/echo_duplicate_services.rb

src/ruby/pb/grpc/testing/metrics_services.rb

src/ruby/pb/src/proto/grpc/testing/empty.rb

src/ruby/pb/src/proto/grpc/testing/messages.rb

src/ruby/pb/src/proto/grpc/testing/test.rb

src/ruby/pb/src/proto/grpc/testing/test_services.rb

src/ruby/qps/src/proto/grpc/testing/services_services.rb