README: revamp

README.md

@@ -1,4 +1,28 @@
+![Elm package](https://img.shields.io/elm-package/v/cachix/elm-hashcash)
+
 Implements [HashCash](https://en.wikipedia.org/wiki/Hashcash) in Elm to
 prevent spammers abusing a resource.
 
-[Install devenv](https://devenv.sh/getting-started/) and `devenv shell`.
+HashCash hashes your data with a `sha256` and appends a nonce.
+
+It then verifies that the hash has N number of leading zeros, which is the difficulty level.
+
+If it doesn't match, it increases the nonce by 1 and retries.
+
+The more leading zeros you want, the longer it takes to find the hash.
+
+Here's an example how to calculate the nonce and send it over with the data:
+
+```elm
+let 
+  data = "example data"
+  difficulty = 3
+  nonce = findNonce difficulty data
+in { nonce = nonce 
+   , data = data
+   }
+```
+
+### Development
+
+[Install devenv](https://devenv.sh/getting-started/) and `devenv shell elm-test`.