Update README.md

git add README
# Stages your README file, adding it to the list of files to be committed

git commit -m 'first commit'
# Commits your files, adding the message "first commit"

# adds all files that are in your current directory and which you've
# recently changed to the "staging area" (ie. they're "ready to commit")
$ git add -A

# commits all the "staged" files into your local repository
$ git commit -m "update README"

# pushes your local repository up to your remote one on Github
$ git push origin master