Improvements to build instructions (perhaps sokoban specific)

[nickgirardo]

I just got sokoban building successfully and there were a couple issues I ran into during the process:

• make import was required for first build. While the readme does describe make import's function, it does not note that it is required to for a build. This could be improved by noting the need to run make import in the readme or perhaps by having the generated assets as a dependency of the bin.
• Running npm install in scripts/converters was necessary, else the program would fail on a missing dependency minimist. I also ran npm install in scripts/sokoban but I'm not sure this was necessary. Perhaps a dummy rule could be created to install all js dependencies? Unsure what your thoughts are on this. In theory you could just run npm install on all the directories for each build as it is fairly fast when there is no work to be done. Here's a quick output from hyper fine:

  Time (mean ± σ):     767.5 ms ± 210.7 ms    [User: 671.4 ms, System: 64.8 ms]
  Range (min … max):   642.0 ms … 1275.7 ms    10 runs
 
  Warning: Statistical outliers were detected. Consider re-running this benchmark on a quiet PC without any interferences from other programs. It might help to use the '--warmup' or '--prepare' options.

This is for one dir, so it isn't no time at all by any means