Add note for contributors to issue template
Add note for contributors to issue template

People open a lot of github issues to propose features or ask for help.
This commit adds a note to the issue template explaining that we use
github issues for bugs only.

Change-Id: Idac1423eb8d40a7aacebe501e113b28d385ce9ae
Reviewed-on: https://gerrit.instructure.com/145368
Reviewed-by: Matthew Edwards <af4636458a6324015a1b5ec4bff45dafe667fa2b@instructure.com>
Product-Review: Matthew Edwards <af4636458a6324015a1b5ec4bff45dafe667fa2b@instructure.com>
QA-Review: Matthew Edwards <af4636458a6324015a1b5ec4bff45dafe667fa2b@instructure.com>
Tested-by: Matthew Edwards <af4636458a6324015a1b5ec4bff45dafe667fa2b@instructure.com>
Tested-by: Jenkins

djbender/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms