re: adding src/README.md

[matthew green <mrg%eterna.com.au@localhost>]

one comment in general, not this specific instance:

> - Why "VAX" and "M68k" are capitalized while "arm64" and "amd64" are
>    not? Why don't you use "aarch64" instead of "arm64"? How do you
>    choose options for build.sh (what happens if they don't have ~/obj)?
>    etc.

please, use arm64 in any public documentation and avoid using
the confusing "aarch64" anywhere that doesn't _need_ it.

we don't want to repeat the "amd64" problem where people don't
install it on 64 bit intel system because it says amd.

thanks.


.mrg.