docs(readme): add arch screenshot preview

Add a visual screenshot of the dotfiles setup to the README for better preview of the configuration.

Author: sabertazimi

.github/screenshots/arch.png

@@ -27,6 +27,8 @@
 Hackable personal dotfiles managed with [`chezmoi`](https://github.com/twpayne/chezmoi)
 (`/ʃeɪ mwa/`).
 
+![Dotfiles](./.github/screenshots/arch.png)
+
 ## Installation
 
 Set up new machine: