Add Desktop Linux subcategory under Linux category

[friendly-rabbit-35]

This idea was discussed on Matrix, but I'm also documenting it here for reference.

Friendly Rabbit: thoughts on creating a subcategory for desktop linux to make things somewhat cleaner and easier to navigate? there are quite a few articles in the linux category that are not about desktop linux

wj25czxj47bu6q (A): Good idea but I don't think PaperMod would support it nicely. Soon™ I will redo the theme from scratch to burn Tommy's eyes and implement coherent design