Default to paths relative to `${KIPRJMOD}`

[der.ule]

@Rene_Poschl has written a great set the tutorials about library management in the FAQ section of the forum, the general idea is described here:

Library management in KiCad version 5

Disclaimer: screenshots taken in nightly from between version 5.0 and 5.1. Version 5.0.x looks slightly different. Version 5.1.x will look like the screenshots show. This is a detailed lecture. If you want to know how to simply add some assets you downloaded to KiCad then you can read the shorter tutorial How to get a downloaded symbol, footprint or full library into KiCad version 5? Summary KiCad does not automatically detect libraries! There is no special library location (you might still ca…

and the specific idea for a team setup would be this:

Project and libary setup for sharing and collaboration (KiCad version 5)

Introduction This information is written with KiCad version 5 in mind. There are at least two schools of thought how to best set up your project and libraries for sharing or collaboration regarding library management. One can either have mainly global libraries or exclusively local libraries. These are of course the extreme ends of the spectrum. Understanding both of them should allow you to find the best mix that best fits your needs. For a detailed lecture about library management read Libra…

the basic idea is that each user would need to define the environment variables locally and on the repository use only the variable names for the paths.

Note that the FAQs were written for the current stable version of KiCAD (v5.1.x) it is probable that in this year the next KiCAD versions (v6 currently 5.99 for testing) will be released and there some point will be different.