README update

README.md

@@ -1,3 +1,24 @@
 # kek
 
-Work-in-progress Erlang implementation of keccak
+This is a working production-quality implementation of Keccak (SHA-3)
+written in pure Erlang.
+
+**You probably want to use
+[erlang-sha3](https://git.qpq.swiss/QPQ-AG/erlang-sha3)**
+([alternate link](https://git.harpending.org/pharpend/erlang-sha3)),
+which
+
+- defaults to a NIF written in C
+- uses the Erlang implementation from this repository as a fallback
+
+You can use the `otpr/erlang-sha3` zomp package.
+
+### Files
+
+- `kek.erl` - Keccak written in "maximally straightforward" Erlang
+- `kek_fast.erl` - kek.erl with some loopy routines inlined
+- `rc.erl` - scratch file to compute Keccak "round constants"
+
+### Acknowledgements
+
+Hans Svensson provided crucial input and also wrote `kek_fast.erl`.