Update starting jekyll

$:~/git_repo/rubygems.github.com$ jekyll --server
       Deprecation: Jekyll now uses subcommands instead of just switches. Run `jekyll help' to find out more.
       Deprecation: The --server command has been replaced by the 'serve' subcommand.
invalid option: --server
Merge pull request #9 from knappe/patch-1

Update starting jekyll documentation