sw0813 / learngit-1

推送请注意：只接受能被自动Merge的Pull Request

Git is a distributed version control system.
Git is a free software distributed under the GPL.
Git has a mutable index called stage.
Git tracks changes of files.
Creating a new branch is quick and simple.
Git can merge branches.
"test pull request." 
update by wk
update by frogy