update rake task description

Author: hone

Rakefile

@@ -13,7 +13,7 @@ Rake::Task[:mruby].invoke unless Dir.exist?(mruby_root)
 Dir.chdir(mruby_root)
 load "#{mruby_root}/Rakefile"
 
-desc "compile binary"
+desc "compile all the binaries"
 task :compile => [:mruby, :all] do
   %W(#{MRUBY_ROOT}/build/host/bin/#{APP_NAME} #{MRUBY_ROOT}/build/i686-pc-linux-gnu/#{APP_NAME}").each do |bin|
     sh "strip --strip-unneeded #{bin}" if File.exist?(bin)