README: Add list of conformance-tested tuf clients

Improve visibility of tested clients and encourage testing.

The list was taken from:
theupdateframework/tuf-conformance#276

kudos to @jku

Signed-off-by: Lukas Puehringer <lukas.puehringer@nyu.edu>

Author: lukpueh

README.md

@@ -15,3 +15,15 @@ Meet the community on the
 - **Location:** [meet.google.com/jhk-cvuf-icd](https://meet.google.com/jhk-cvuf-icd)
 - **Agenda:** [hackmd.io/jdAk9rmPSpOYUdstbIvbjw](https://hackmd.io/jdAk9rmPSpOYUdstbIvbjw)
 - **Calendar:** [www.cncf.io/calendar](https://www.cncf.io/calendar/) 
+
+
+## TUF Clients
+
+TUF clients tested for specification-conformance. See the
+[TUF conformance test suite](https://github.com/theupdateframework/tuf-conformance)
+for details and instructions to get tested.
+
+[![python-tuf](https://img.shields.io/github/actions/workflow/status/theupdateframework/python-tuf/conformance.yml?branch=develop&label=python-tuf)](https://github.com/theupdateframework/python-tuf/actions/workflows/conformance.yml?query=branch%3Adevelop)
+[![tuf-js](https://img.shields.io/github/actions/workflow/status/theupdateframework/tuf-js/conformance.yml?branch=main&label=tuf-js)](https://github.com/theupdateframework/tuf-js/actions/workflows/conformance.yml?query=branch%3Amain)
+[![sigstore-ruby](https://img.shields.io/github/check-runs/sigstore/sigstore-ruby/main?nameFilter=TUF%20Ruby%203.4%20%2F%20ubuntu-latest&label=sigstore-ruby)](https://github.com/sigstore/sigstore-ruby/actions/workflows/ci.yml?query=branch%3Amain)
+[![sigstore-java](https://img.shields.io/github/actions/workflow/status/sigstore/sigstore-java/tuf-conformance.yml?branch=main&label=sigstore-java)](https://github.com/sigstore/sigstore-java/actions/workflows/conformance.yml?query=branch%3Amain)