Document how to create the ~/.carton/static directory when using unreleased versions.

[deatondg]

I built carton by simply git cloneing and running swift build, but carton dev kept complaining about the SHA256’s of the static archive it was downloading. It took me awhile to figure out what I was supposed to

npm install
npm run build

and then copy the resulting static directory into the right place. The start-up experience would be nicer if users were warned about this in advance, in case they need to run an unreleased version.

[disc0infern0]

Thankyou so much for this issue - and solution. I too had built carton from source, and after getting it to build, I wasn't sure where to put the binaries, since some clash with those from swift. I put the carton executable in $HOME/bin, and then had the same trouble as you with unmatching SHA256's. I would never have guessed that npm had to be installed. thankyou