docs: clarify contributor wall eligibility (#12978)

* docs: clarify contributor wall eligibility

* docs: preserve contributor wall wording

CONTRIBUTING.md

@@ -173,3 +173,5 @@ Small PRs are easier to review and merge.
 - [Official docs](https://dbxio.com/en/docs/what-is-dbx)
 
 Merged contributors appear on the [DBX contributors wall](https://dbxio.com/en/community).
+
+The wall recognizes a GitHub account after it authors at least one PR merged into `t8y2/dbx`; commit counts alone do not qualify. Open your PR from the account you want credited.

CONTRIBUTING.zh-CN.md

@@ -172,3 +172,5 @@ make docs
 - [官方文档](https://dbxio.com/cn/docs/what-is-dbx)
 
 合并后的贡献者会出现在 [DBX 贡献墙](https://dbxio.com/cn/community)。
+
+贡献墙按发起并合入 `t8y2/dbx` 的 PR 的 GitHub 账号认定；仅有提交记录不满足展示条件。请用希望署名的账号创建 PR。