Add a issue template.

Add a issue template for higher quality issues.

.github/ISSUE_TEMPLATE.md

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+
+### Please read and check all.
+
+- [ ] I have a issue with directly by LifeMC-API, not other extensions or my mistake.
+- [ ] I searched other issues for not opening a duplicate issue.
+- [ ] I think this issue is fixable and the issue is caused directly by LifeMC-API or its sub-projects.
+
+### What is the issue? (Write long, describe all.)
+
+[Write your issue here. Write long, Describe the all issues and what you have do.]
+
+### What happened and what you expect to happen?
+
+[Write what happened and what you expect to happen here.]
+
+### What is the "real" issue? (Write short.)
+
+[Write your issue here. Write short. Describe the only real issue.]
+
+### What is the cause you think?
+
+[Write what is the cause of issue you think. You can skip this.]
+
+### Other Notes
+
+[Write your notes here, if none, skip this.]
+
+### Finally
+
+[Delete all these description sections in the brackets.]