doc for matchit.vim v1.13
Update README.md, add 'matchit'

更新 README.md，增加 Vim 自带插件 matchit 的中文文档

该文档取自
https://github.com/vimcn/matchit.vim.cnx/blob/master/doc/matchit.cnx
该版本的提交为
https://github.com/vimcn/matchit.vim.cnx/commit/f0ba6d084807de97956d4168b2956f0da6286c28
对应的 matchit 插件为
https://code.google.com/p/vim/source/browse/runtime/macros/matchit.vim
对应的英文文档为
https://code.google.com/p/vim/source/browse/runtime/macros/matchit.txt
Merge pull request #3 from Firef0x/matchit

Feature Request: Add doc for plugin 'Matchit'