[contributing] Add issue template

Author: woojiahao

.github/ISSUE_TEMPLATE/request_exercise_repository.md

@@ -0,0 +1,28 @@
+---
+name: Request for Exercise Repository
+about: Creating a new exercise for Git-Mastery and require a remote repository on the Git-Mastery organization? Request one here.
+title: [Exercise Repository Request]
+labels: exercise-repository-request
+assignees: woojiahao
+---
+
+# Exercise Repository Request
+
+## Exercise Objectives
+
+- What are the objectives of this exercise?
+- Which tour and lesson does this exercise belong to?
+- What are the core concepts tested in this exercise?
+
+## Use of Exercise Repository
+
+- What will the exercise repository be used for?
+
+## Exercise Grading Setup
+
+- How is the exercise setup for the exercise?
+- What is the grading scheme for the exercise?
+
+## Checklist
+
+- [ ] Have you verified that this exercise does not already exist or is not currently in review?