In most linuxes that I used (ubuntu/centos) they are added to /usr/share/applications to make it an item available in the start menu. but requires sudo access, and since most people use apt or yum to install these packages, it is not issue for them, but it would be for us.
I was hoping someone more knowledgeable than me with Linux can clarify if it is possible to do this in user space, without sudo access and in a WM generic way. I think some files written under .config.
I am not sure about the absolute vs relative path issue. I always put the full path to the executable. But in our case it is not predictable.