Add reference to pcloudcc-service (#170)

* Fix #162: Add distro-agnostic mbedtls detection

- Use pkg-config to dynamically detect mbedtls variants (mbedtls3.x, mbedtls)
- Fallback to /usr/local if pkg-config unavailable
- Tested on Fedora 41 (mbedtls3.6), Arch Linux (mbedtls 3.6.5), Debian Bookworm, and Slackware
- Eliminates need for hardcoded version-specific paths

* Add reference to pcloudcc-service

Closes #159

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Co-authored-by: Levi Neely <lkn@darkstar.example.net>

README.md

@@ -43,3 +43,8 @@ file.
 - [Log Management Guide](./LOG-MANAGEMENT.md): Read this to configure log rotation,
   cache size limits, and custom log paths. To set up automatic log rotation, copy
   `pcloudcc.logrotate` to `/etc/logrotate.d/pcloudcc`.
+
+- [pcloudcc-service](https://github.com/ibressler/pcloudcc-service): Container-based
+  systemd service for running `pcloudcc` in userspace with podman. Includes multi-stage
+  Dockerfile that builds `pcloudcc` from source and Quadlet systemd unit for automated
+  background syncing.