docs(readme): link to upstream (#17)

Signed-off-by: Chris Gianelloni <[email protected]>

Author: wolf31o2

README.md

@@ -1 +1,4 @@
-# docker-cardano-wallet
+# docker-cardano-wallet
+
+Builds [Cardano Wallet](https://github.com/cardano-foundation/cardano-wallet)
+from source on Debian.