Summary:
This template reminds the users to use issues only for bug reports. The template is written according to the github guidelines at https://help.github.com/articles/creating-an-issue-template-for-your-repository/
Closes https://github.com/facebook/rocksdb/pull/2948

Differential Revision: D5943558

Pulled By: maysamyabandeh

fbshipit-source-id: c83b5d211ea8e334107141967689b2f0c453bbc9