docs: add back-navigation link to cpp-linter hub (#128)

Adds `← Back to cpp-linter hub` link near the top of the README for
easier cross-project navigation.

Author: shenxianpeng

README.md

@@ -5,6 +5,7 @@
 ![Maintenance](https://img.shields.io/maintenance/yes/2026)
 [![CI](https://github.com/cpp-linter/clang-tools-docker/actions/workflows/CI.yml/badge.svg)](https://github.com/cpp-linter/clang-tools-docker/actions/workflows/CI.yml)
 [![Docker Scout](https://github.com/cpp-linter/clang-tools-docker/actions/workflows/docker-scout.yml/badge.svg)](https://github.com/cpp-linter/clang-tools-docker/actions/workflows/docker-scout.yml)
+[![cpp-linter hub](https://img.shields.io/badge/%F0%9F%8F%A0_cpp--linter_hub-%E2%86%90_home-22863a)](https://cpp-linter.github.io/)
 
 🐳 **Clang Tools Docker Image**: This Docker image comes pre-installed with essential clang tools, including `clang-format` and `clang-tidy`.