Add PR and issue templates

.github/ISSUE_TEMPLATE.md

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+<!--- Provide a general summary of the issue in the Title above -->
+
+## Detailed Description
+<!--- Provide a detailed description of the change or addition you are proposing -->
+
+## Context
+<!--- Why is this change important to you? How would you use it? -->
+<!--- How can it benefit other users? -->
+
+## Possible Implementation
+<!--- Not obligatory, but suggest an idea for implementing addition or change -->
+
+## Your Environment
+<!--- Include as many relevant details about the environment you experienced the bug in -->

.github/PULL_REQUEST_TEMPLATE.md

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+Fixes #
+
+## Requirements
+
+All new code should be covered with tests, documentation should be updated. CI should pass.
+
+## Description of the Change
+
+<!--
+
+Why this change is important?
+
+-->
+
+## Checklist
+
+- [ ] unit-test added (if change is algorithm)
+- [ ] functional test added/updated (if change is functional)
+- [ ] man page updated (if applicable)
+- [ ] documentation updated
+- [ ] author name in `AUTHORS`