[skip ci] Sync links to internal docs files

For now, these two are still in the docs folder. See phpGH-13536.

Author: petk

README.md

@@ -132,8 +132,8 @@ contribute:
 - [Contributing to PHP](/CONTRIBUTING.md)
 - [PHP coding standards](/CODING_STANDARDS.md)
 - [Internal documentation](https://php.github.io/php-src/)
-- [Mailing list rules](/docs-old/mailinglist-rules.md)
-- [PHP release process](/docs-old/release-process.md)
+- [Mailing list rules](/docs/mailinglist-rules.md)
+- [PHP release process](/docs/release-process.md)
 
 ## Credits