Service for rTorrent.

[lindely]

Description

I'm setting up homer for use as my browser start page and was adding links to various sites and (self-hosted) services. I thought it'd be interesting to include transfer rates and number of torrents in the link to my rTorrent web UI, so I made a service for that. I have also updated the customservices.md with instructions for the new service.

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [X] I've read & comply with the contributing guidelines
• [X] I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• [X] I have made corresponding changes to the documentation (README.md).
• [X] I've checked my modifications for any breaking changes, especially in the config.yml file