Add some details to the roadmap

Author: Priya Wadhwa

ROADMAP.md

@@ -1,3 +1,8 @@
 # Tekton Chains Roadmap
 
-COMING SOON
+This is a list of some of the things we hope to accomplish in 2021:
+
+* [Hardened Tekton](https://github.com/tektoncd/chains/issues/87) -- Integration with SPIFFE/SPIRE
+* [Sigstore Integration] -- Integrating with [cosign](https://github.com/sigstore/cosign), [rekor](https://github.com/sigstore/rekor), and [fulcio](https://github.com/sigstore/fulcio) to further secure the Tekton supply chain
+* Signing other types of artifacts, in addition to the available TaskRuns and OCI images [#124](https://github.com/tektoncd/chains/issues/124)
+* Tekton Chains Beta