store username and password to prevent git asks me every time

Sometimes I push my github.io repository, git asks me enter user name and password. It’s so waste time. Because I need to enter that every time. After I set the credential.helper option to store, then fill in username and password again. I will don’t enter username and password next time.

> git config --global credential.helper store
> git push
Username for 'https://github.com':
Password for 'https://[USER NAME]@github.com':