Add Proxmox Backup Server to Backups (#494)

README.md

@@ -109,6 +109,7 @@
 - [Duplicati](http://www.duplicati.com) - Multiple backends, encryption, web-ui and multi-OS backup tool.
 - [Duplicity](https://duplicity.gitlab.io/) - Encrypted bandwidth-efficient backup using the rsync algorithm.
 - [Elkarbackup](https://github.com/elkarbackup/elkarbackup) - Backup solution based on RSnapshot with a simple web interface
+- [Proxmox Backup Server](https://www.proxmox.com/en/proxmox-backup-server) - Proxmox Backup Server is an enterprise-class, client-server backup solution thatis capable of backing up virtual machines, containers, and physical hosts. ([Source Code](https://www.proxmox.com/en/downloads/category/isoimages-pbs)) `GPL-3.0` `Rust`
 - [rclone](https://rclone.org/) - a command line program to sync files and directories to and from several cloud storage systems/providers.
 - [Rdiff-backup](http://www.nongnu.org/rdiff-backup/) - An easy A remote incremental backup of all your files.
 - [Restic](https://restic.net/) - Secure, remote backup tool. Designed to be easy, fast, verifiable and efficient.