Add UCAN version badge and status notice (#638)

Author: bgins

hs-ucan/README.md

@@ -1,3 +1,5 @@
 # hs-ucan
 
-TODO
+![UCAN](https://img.shields.io/badge/UCAN-v0.3.1-blue)
+
+This UCAN implementation is not actively maintained. If you would like to help to update it to the latest UCAN specification, please reach out on the UCAN Discord in the `#hs-ucan` channel: https://discord.gg/zSfgeHhKxA.