feat: update spec

Author: shenxianpeng

content/_index.md

@@ -41,6 +41,8 @@ DevOps Maturity Specification is a set of guidelines for DevOps best practices,
 | Reporting          | D601   | Notifications & Alerts[^18]      | 🟢     |
 |                    | D602   | Attached Reports[^19]            | 🟢     |
 
+For details on maturity code, please refer to [Maturity Code Map](https://devops-maturity.github.io/about/#maturity-code-map).
+
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