feat: add configuration documentation and update TODO checklist

Add detailed configuration documentation in README, describing TOML files, their purpose, and usage. Update the TODO checklist to reflect completed items and remove outdated entries.

README.md

@@ -56,6 +56,46 @@ cd ~/.config/Modus
 
 <h2><sub><img src="https://raw.githubusercontent.com/Tarikul-Islam-Anik/Animated-Fluent-Emojis/master/Emojis/Travel%20and%20places/Rocket.png" alt="Rocket" width="25" height="25" /></sub> Todo</h2>
 
+## Configuration
+
+Config files are in `config/` directory, using TOML format:
+
+| File                   | Purpose                |
+| ---------------------- | ---------------------- |
+| `config/config.toml`   | Main app configuration |
+| `config/mods.toml`     | Custom mod definitions |
+| `config/launcher.toml` | Launcher settings      |
+| `config/dock.toml`     | Dock pinned apps       |
+
+## Custom Mods
+
+Define panel buttons that run commands or show dropdowns in `config/mods.toml`:
+
+```toml
+[Mods.terminal]
+icon = "terminal.svg"
+icon-size = 16
+order = 1
+on-clicked = "kitty"
+
+[Mods.color-picker]
+icon = "misc/color-picker.svg"
+icon-size = 22
+order = 0
+on-left = "hyprpicker -a -n -f hex && sleep 0.1 && ..."
+on-middle = "hyprpicker -a -n -f rgb && sleep 0.1 && ..."
+on-right = "hyprpicker -n -f hsv | wl-copy -n && sleep 0.1 && ..."
+```
+
+- `icon` — SVG filename in `src/assets/icons/`
+- `icon-size` — defaults to 16
+- `order` — button position (lower = first)
+- `on-clicked` — shell command on any click
+- `on-left`, `on-middle`, `on-right` — per-mouse-button commands (optional)
+- `options` — dropdown menu entries (optional, each with `label` + `on-clicked`)
+- Supports `&&`, `|`, and full shell syntax (runs via `sh -c`)
+- File monitoring enables live reload — edit `mods.toml` and changes apply instantly
+
 ## Manual Installation
 
 ```bash
@@ -74,7 +114,7 @@ uv run start
 - [x] Music Player
 - [x] Desktop Widgets
 - [x] New Launcher (like Spotlight)
-- [ ] Settings
+- [x] Settings
 - [x] ~~Magnifier hover effect on Dock~~
 - [x] ~~New Application Switcher~~
 - [x] Panel Widget