Telekom.de using Knative: Find the contact point and add them to Adopters.md

[Naina Singh]

https://www.telekom.de/start using Knative: The serving parts for their internal "rest services". Motivation was cost-saving, since the services just ran while some batches were executed, which feed data into those. The transition to Knative was easy, and they like it, since it does make things easier for them.