add reason for deprecation

Author: thelamer

readme-vars.yml

@@ -3,6 +3,7 @@
 # project information
 project_name: rdesktop
 project_deprecation_status: true
+project_deprecation_message: "These images were originally created for Apache Guacamole-based Webtop, but since transitioning to an in house web-native protocol, they are no longer maintained. RDP users should seek alternatives while others are advised to transition to [Webtop](https://github.com/linuxserver/docker-webtop)."
 project_lsio_github_repo_url: "https://github.com/linuxserver/docker-{{ project_name }}"
 full_custom_readme: |
   {% raw -%}