add readme and knob styles

README.md

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+# Knob Widget
+
+Simple knob widget for egui.
+
+## Features
+
+- Adjustable size, font size, and stroke width.
+- Customizable colors for the knob and line.
+- Label positions (Top, Bottom, Left, Right).
+- Two styles: Wiper and Dot.
+
+## Installation
+
+To use the Knob widget in your project, add the following to your `Cargo.toml`:
+
+```toml
+[dependencies]
+egui = "0.30"
+```
+
+## Usage example
+
+```rust
+use egui::{Color32, Context};
+use egui_knob::Knob;
+
+// ..
+
+let mut value: f32 = 0.5;
+let knob = Knob::new(&mut value, 0.0, 1.0, KnobStyle::Wiper)
+    .with_size(50.0)
+    .with_font_size(14.0)
+    .with_stroke_width(3.0)
+    .with_colors(Color32::GRAY, Color32::WHITE)
+    .with_label("Volume", LabelPosition::Top);
+
+egui::CentralPanel::default().show(ctx, |ui| {
+    ui.add(knob);
+});
+```