ISSUE_TEMPLATE.md

If this is a bug report, please fill in the blanks:

*  I am using the ___________ browser.
*  My computer's OS is ___________.
*  I'm running Metabase ___________. [locally from the JAR / locally with the Mac App / on AWS / on Herkou / etc.]
*  My database is ___________.
*  My Metabase version is ___________.