We have no installation routines for Linux. There are too many distributions using different locations for this stuff.
Placing resources to their preferred locations is what the distribution maintainer usually do.
The LibreCAD application on Linux search different places for the resources like fonts, libraries, plugins, translations.
What is your intention to build from source?
If you just want a newer version I recommend to use or AppImage distribution.
Some Red Hat based distributions started to switch over to 2.2.0 release candidates lately.
I don' t know when Debian and derivates will follow, but at least when we release 2.2.0 finally soon. Then you can use
apt to install and automatic updates.
When your intention is to modify code it is best to use librecad from unix folder, as it contains everything it needs.
For the above said reasons, we also have no installation instructions for Linux.
If you anyway want to install your built version manually, you can have a look into
CI/build-appimage.sh. Assume that
appimage/ is the root folder, then you see folders created under
/usr and which resources are copied to these locations.
investing less than half an hour into Search function can save hours or days of waiting for a solution