doc: Maybe specify existence check, safe to rerun script w/o getting dupes?

[chipbite]

Hi!

I noticed in the code for add it seems you are checking if the path to be added already exists.

An idea is to add a short description of this in the readme?

[coolaj86]

Yes, it was intended to be idempotent - although as you've discovered it doesn't always work that way to due the mix of / and \ handling (trying to be POSIX-friendly).