Document how to provide dictionaries and seed corpus to fuzzers

Hi, first of all thanks for all the awesome work you've put into this project really appreciate it.

For several of my fuzzers I've created [dictionaries](https://llvm.org/docs/LibFuzzer.html#dictionaries) and/or have large number of sample files which I obviously would like the fuzzers to take advantage of.

I've looked through the documentation [here](https://google.github.io/clusterfuzzlite) but was not able to find the answers there so maybe someone here can help me.