Add a PR template. (#2344)
Add a PR template. (#2344)

In order to remind to attach tests and to not commit any of the distribution file.
alanhamlett/c3,alanhamlett/c3,c3js/c3,alanhamlett/c3,masayuki0812/c3,masayuki0812/c3,c3js/c3,c3js/c3,c3js/c3