Adjust instructions for Yambar config

[schultzdavid]

When trying to run tiny-wlhs on my NixOS system, I first had to add a yambar config file, e.g. $HOME/.config/yambar/config.yml, and e.g. with content the sample configuration from the yambar repo:

bar:
  height: 26
  location: top
  background: 000000ff

  right:
    - clock:
        content:
          - string: {text: , font: "Font Awesome 6 Free:style=solid:size=12"}
          - string: {text: "{date}", right-margin: 5}
          - string: {text: , font: "Font Awesome 6 Free:style=solid:size=12"}
          - string: {text: "{time}"}

So the README should explain that one has to do this. Or, even better, a config file should be created automatically. However, it should then certainly not be located in $HOME/.config or so, but somewhere within the cloned tiny-wlhs repo. According to man 5 yambar, config files are searched for in this order:

$XDG_CONFIG_HOME/yambar/config.yml
$HOME/.config/yambar/config.yml

I don't understand direnv and the manner in which it is used in this project that well yet, but maybe one can use it to set XDG_CONFIG_HOME to some subdirectory of this repo that then contains the config.yml for yambar. This variable currently doesn't seem to be set (printenv | grep XDG_CONFIG only gives something for XDG_CONFIG_DIRS).