Missing font requirement: PowerlineSymbols

[progandy]

The built-in themes slick, solarized-dark, and modern use a powerline symbol as the separator. This character is not part of FontAwesome, but requires the installation of the font PowerlineSymbols.
On Arch Linux, it is available in the package powerline-fonts

[LuchiLucs]

Confirmed, the powerline-fonts package installation resolved this issue.
Here are two comparison screenshots, before and after the package installation:
before
after

[greshake]

Thanks for pointing that out, don't know how noone else noticed before :D Will add some remarks in the README as soon as I can, if you guys want you can open a PR with changes to the README (it'd be quicker).

[greshake]

Happy with these changes?

[LuchiLucs]

Yes, I would be happy to help with PR and edit the README file or add some documentation but I am new to linux and github, so I have so many things I need to learn first and I am always busy. Maybe in the future I will contribute a bit ^^