adding Issue/PR templates

.github/ISSUE_TEMPLATE.md

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+> This is the place to report a bug, ask a question, or suggest an enhancement.
+
+> This is also the place to make a discussion before creating a PR.
+
+> If this is a bug report, please provide a test case (e.g., your table definition and gh-ost command) and the error output.
+
+> Please use markdown to format code or SQL: https://guides.github.com/features/mastering-markdown/
+
+> And please understand if this issue is not addressed immediately or in a timeframe you were expecting.
+
+> Thank you!

.github/PULL_REQUEST_TEMPLATE.md

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+## A Pull Request should be associated with an Issue.
+
+> We wish to have discussions in Issues. A single issue may be targeted by multiple PRs.
+> If you're offering a new feature or fixing anything, we'd like to know beforehand in Issues,
+> and potentially we'll be able to point development in a particular direction.
+
+Related issue: https://github.com/github/orchestrator/issues/0123456789
+
+> Thank you! We are open to PRs, but please understand if for technical reasons we are unable to accept each and any PR
+
+### Description
+
+This PR [briefly explain what is does]
+
+> In case this PR introduced Go code changes:
+
+- [ ] contributed code is using same conventions as original code
+- [ ] code is formatted via `gofmt` (please avoid `goimports`)
+- [ ] code is built via `./build.sh`
+- [ ] code is tested via `go test ./go/...`