feat: added nerd font symbols for tmux status bar

[ofseed]

Comparing different tmux status bar theme, I found that many of them use nerd font and it makes them more beautiful. Inspired by this, I added nerd font symbols to the status bar.

[folke]

I just pushed a big update, so please rebase on main.

Instead of changing the files directly, you should change the template.

Please refer to the bottom section of the readme.