`sed` on `Makefile` looks wrong

[hatoo]

Hi, thanks for publishing this repository! During testing on my side, it seems that the Makefile is wrong.

I'm not very familiar with sed, but I think https://github.com/adam-maj/tiny-gpu/blob/de7cf22d630fdbad7c1762708665e3370002681f/Makefile#L14

should be

sed -i '1s/^/`timescale 1ns\/1ns\n/' build/gpu.v

and I've also noticed that running a simulation requires compiling https://github.com/zachjs/sv2v from the source because it seems using https://github.com/zachjs/sv2v/blob/261beffd0f4dd26bd1a19d574bbcc2caabba2eaa/CHANGELOG.md?plain=1#L42 which is not released yet. I think this information is good to add somewhere in README.

[xianbaoqian]

I managed to run this on my macbook. Created a PR with some instructions: https://github.com/adam-maj/tiny-gpu/pull/2