Update build instructions regarding .tarball-version

[Lex Spoon]

This patch helps with something you need the first time you check out a
Bison repository. I've done this two times in my life and had trouble both
times.

I don't really know for sure what the best suggestion would be, but it
seems important to give people some kind of instructions on how to get over
this hump. What I suggest in the patch is to create a .tarball-version file
with a random version number in it.

It would seem a little better if UNKNOWN could be used, or some other
string that makes it obvious that this is a development build. However,
Gnits doesn't seem to allow for that, and the bootstrap instructions are
currently invoking Gnits.

Lex Spoon

tarball-version.patch
Description: Text Data