Restyle Add instructions on how to add trace events

src/trace/README.md

@@ -0,0 +1,40 @@
+# Matter tracing
+
+Matter tracing provides a tool for applications to trace information about the
+execution of the application. It depends on
+[pw_trace module](https://pigweed.dev/pw_trace/).
+
+## How to add trace events
+
+1. Include "trace/trace.h" in the source file.
+2. Add "\${chip_root}/src/trace" as deps in BUILD.gn.
+3. Add MATTER*TRACE_EVENT*\* in functions to be traced.
+
+## Example
+
+```
+#include "pw_trace/trace.h"
+
+  void SendButton() {
+    MATTER_TRACE_EVENT_FUNCTION();
+    // do something
+  }
+
+  void InputLoop() {
+    while(1) {
+      auto event = WaitNewInputEvent()
+      MATTER_TRACE_EVENT_SCOPE("Handle Event");  // measure until loop finished
+      if (event == kNewButton){
+        SendButton();
+        MATTER_TRACE_EVENT_END("button");  // Trace event was started in ButtonIsr
+      } else {
+        MATTER_TRACE_EVENT_INSTANT("Unknown event");
+      }
+    }
+  }
+
+  void ButtonIsr() {
+    MATTER_TRACE_EVENT_START("button");
+    SendNewInputEvent(kNewButton);
+  }
+```