Added PR template

Author: sidoruka

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,19 @@
+# Description
+
+## Background
+
+*What idea led to this PR, general task description*
+
+## Changes
+
+*What was changed in the system to accomplish the task*
+
+## Acceptance criteria
+
+*How to check that a task is accomplished, what user shall do to check it*
+
+# Check list
+
+- [ ] Unit tests are provided
+- [ ] Integration tests are provided (if CLI/API was changed)
+- [ ] Documentation is updated