resolve to a default version for each toolchain if already exists

[monshi]

I installed notion on my mac 🎉🚀 and got so excited 💃🕺so that the first thing I did after that was to run node -v in the same directory and I got this error: error: An unknown error has occurred.
I was assuming that if there is no package.json or notion config block then notion will either fall back to a default version of node or will respect my previously installed version of node. By that I mean, when the notion is installed on a machine it can detect and install the global version of my installed toolchain (node, yarn ...) and set them as default versions.

If the expected behavior is not as I assumed, then maybe another option would be showing some instructions/helpful errors instead of error: An unknown error has occurred. I'll be happy to help fixing it as well :)

[charlespierce]

The error message part of this issue has been resolved with the error rework. The pass-through to existing tools is currently in review in #372