@tarunon 僕も英語に自信はないですが、とりあえず修正案考えてみました。

Problems happen when someone who have posted mails to the ML in the past sign up using GitHub authentication. They hope to change their username, but cannot do it after once their accounts were created. I wish there were some additional explaination in the sign up screen, and to get a chance to change the username even if signup is done using github authentication.