github: template for reporting new issues
github: template for reporting new issues

Having a standardized template for bug reports should help the reporters
and the fixers get to a resolution.

Closes chain/chainprv#1670
Reviewers: da39a3ee5e6b4b0d3255bfef95601890afd80709@bobg

chain/chain,chain/chain,chain/chain,chain/chain,chain/chain,chain/chain