added integration section to readme

Author: Geolm

README.md

@@ -47,26 +47,45 @@ leanUI provides a small, cohesive set of widgets:
 Each widget is built with consistent spacing, alignment, and interaction patterns.  
 The goal is not to cover everything, but to make a minimal set look and feel right out of the box.
 
----
-
-## Animation & Easing
+## Animation
 
 Unlike most tiny immediate-mode UI libraries, leanUI has animation built in:
 
 - Hover, press and toggle states are automatically eased over time.
-- Animation framerate independant, uses delta time between frames.
+- Animation framerate independent, uses delta time between frames.
 - No per-widget state is stored — transitions are computed implicitly based on widget identity.  
 
 This gives small UIs a fluid, modern feel without adding complexity to your code.
 
----
-
 ## Layout
 
-Very simple and effective (no rows, no columns)
+Very simple and effective layout (no rows or columns)
 - Horizontal alignment : left, center or right
 - Manually call to ui_newline to make a carriage return
 
+---
+
+## Integration
+
+You just need to add lean_ui.c/h to your project, set the callbacks at init and update input/delta_time each frame.
+
+### Callbacks
+- **draw_box**: The rectangle’s rounded corners are expected to fit entirely within the rectangle’s bounds; no part of the corner should extend beyond x, y, width, or height.
+
+- **draw_text**: Draws text at (x, y). The y coordinate specifies the top, but the text will be centered vertically relative to the font height.
+
+- **set_clip_rect**: Sets a clipping rectangle so that all subsequent drawing is limited to (x, y, width, height). You can ignore this callback if no widget will be drawn outside the window frame.
+
+- **text_width**: Returns the width that the renderer would need to draw the specified text.
+
+
+### Inputs
+
+* **ui_update_mouse_pos**: Should be called each time the mouse moves
+* **ui_update_mouse_button**: Call this function whenever a mouse button changes state. Do not call with button_pressed param if the button remains pressed.
+
+---
+
 ## Example
 
 For a complete and compiling example see [test/test.c](test/test.c)