Update issue templates

.github/ISSUE_TEMPLATE/---improvement-request.md

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+---
+name: "\U0001F340 Improvement request"
+about: An improvement to existing functionality
+title: "[improvement]: "
+labels: improvement
+assignees: ''
+
+---
+
+**1~3 main use cases of the proposed improvement**
+Ex: As a ..., I have many tasks scattered across documents, and I want to have a unified entry to view these tasks.
+
+**Ideas for Solution**
+Ex: A task view can be added to view all tasks.
+
+**what types of users can benefit from using your proposed feature**
+Ex: busy programmer.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.