Check whether inputted ID is duplicated or not when registering
Update README.md
Update README.md
Check whether inputted ID is 3-15 characters long and contains only
letters(a-z), numbers, period(.) and hyphen(-)
Merge pull request #37 from axpower/master

Check whether inputted ID is duplicated or not, only 3-15 characters long and contains only letters(a-z), numbers, period(.) and hyphen(-) when registering