Add categories to readme-vars.yml

Author: quietsy

readme-vars.yml

@@ -7,6 +7,7 @@ project_logo: "https://raw.githubusercontent.com/linuxserver/docker-templates/ma
 project_blurb: |
   [{{ project_name|capitalize }}]({{ project_url }})  is an open source, self-hosted web application for managing a collection of 3D models, particularly focused on 3D printing.
 project_lsio_github_repo_url: "https://github.com/linuxserver/docker-{{ project_name }}"
+project_categories: "3D Printing"
 # supported architectures
 available_architectures:
   - {arch: "{{ arch_x86_64 }}", tag: "amd64-latest"}