README / INSTALL should list requirments

[Ryan C. Gordon]

> E.g. you can't run bootstrap w/o FLAC, as I have just found out. Now
> I have to find the URL for that. That's not hard I guess, but if all
> of this was listed in some sort of document, it would be a plus.

I've added the information to the README (which is slowly becoming worth
reading  :)  ).

bootstrap ran fine without FLAC here when I just tried it...can you tell
me what specifically is causing problems and/or which part of bootstrap
is failing?

--ryan.