Add usage instructions

[larsbrinkhoff]

Hello,

@ZoBoRf, maybe it's still too soon. But when things settle, could you add some usage instructions here. Nothing too detailed, just how to invoke the tools. And maybe if there's something special about how to run Muddle and load the code. No need to explain about GC failures etc.

[ZoBoRf]

https://github.com/ZoBoRf/ZILCH-How-to
https://github.com/ZoBoRf/ZIL-Tool-Chain

[larsbrinkhoff]

Thanks, those are excellent writeups!