Add Trier Center for Digital Humanities (TCDH) to academic map and update TOC

[reginankenchor]

This pull request adds the Trier Center for Digital Humanities (TCDH) to the academic map. TCDH is a research center based at the University of Trier, Germany, and is active in promoting Open Science within the digital humanities.
Changes included:

Added a new Markdown entry: organizations/trier_center_for_digital_humanities.md

Updated index.md to include TCDH under Communities of practice

Updated toc.yml to reflect the new page in the Table of Contents

[RichardLitt]

Thanks Regina.

Ok, high-level: Do you think this should be in here? Why?

I can't find any open source work that they actually do, besides saying that they use open source. What am I missing?

[RichardLitt]

Can't find any OSS on their site.