add info for how it works

HOW_IT_WORKS.md

@@ -1,4 +1,29 @@
-# Data flow diagram
+# INTRODUCTION
+
+```golang
+// build the a donut engine for user's input (ie: srt://server)
+donutEngine := h.donut.EngineFor(reqParams)
+// fetches the server-side stream info (codec, ...)
+serverStreamInfo := donutEngine.ServerIngredients(reqParams)
+// gets the client side media support (codec, ...)
+clientStreamInfo := donutEngine.ClientIngredients(reqParams)
+// creates the necessary recipe (by pass, transcoding from A to B, etc)
+donutRecipe := donutEngine.RecipeFor(reqParams, serverStreamInfo, clientStreamInfo)
+
+// serve asynchronously the server stream to the client web rtc
+go donutEngine.Serve(&entities.DonutParameters{
+	Recipe: *donutRecipe,
+	OnVideoFrame: func(data []byte, c entities.MediaFrameContext) error {
+		return webRTC.SendMediaSample(VIDEO_CHANNEL, data, c)
+	},
+	OnAudioFrame: func(data []byte, c entities.MediaFrameContext) error {
+		return webRTC.SendMediaSample(AUDIO_CHANNEL, data, c)
+	},
+})
+
+```
+
+# DATA FLOW DIAGRAM
 
 ```mermaid
 sequenceDiagram
@@ -29,7 +54,7 @@ sequenceDiagram
     end
 ```
 
-# Core components
+# CORE COMPONENTS
 
 ```mermaid
 classDiagram