Register stabilization report template

Author: jieyouxu

src/SUMMARY.md

@@ -50,7 +50,8 @@
 - [Walkthrough: a typical contribution](./walkthrough.md)
 - [Implementing new language features](./implementing_new_features.md)
 - [Stability attributes](./stability.md)
-- [Stabilizing Features](./stabilization_guide.md)
+- [Stabilizing language features](./stabilization_guide.md)
+    - [Stabilization report template](./stabilization_report_template.md)
 - [Feature Gates](./feature-gates.md)
 - [Coding conventions](./conventions.md)
 - [Procedures for Breaking Changes](./bug-fix-procedure.md)