[doc] add issues and pull-request templates #98
Description
pretty standard stuff, maybe reuse a template or use a template generator?
Issue template should thank the user and ask them:
- to run
go env - to share Go code
- to explain what they did
- what they were expecting
- what happened instead
PR template should just thank the user and ask them to link the PR to a specific issue (and possibly to have created that issue first)