README: add instructions/steps on how to use this together with `google/clasp`

[stephenchu]

Hello,

I would love to see some instructions on how to get this generated file/folder structure skeleton to work well with google/clasp's set up, specifically where to place its .clasp.json, appsscript.json, etc, relative to the src folder of typescript-library-starter, so that clasp push would work perfectly.

TIA, and good work!