Add readme.md

readme.md

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+# How to
+
+## At the middleware
+```go
+func (h *Handler) LogMW(next http.HandlerFunc) http.HandlerFunc {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var (
+			ctx      context.Context = rctx.AssignRequestID(r.Context())
+			rWithCtx *http.Request   = r.WithContext(ctx)
+
+			reqID  string = rctx.GetRequestID(ctx)
+			values        = r.URL.Query()
+
+			attrs []slog.Attr = []slog.Attr{
+				slog.String("req id", reqID),
+				slog.String("method", r.Method),
+				slog.String("URI", r.RequestURI),
+				slog.String("remote", r.RemoteAddr),
+			}
+		)
+
+		// Append query params as logger info:
+		for i, value := range values {
+			switch {
+			case len(value) == 1:
+				attrs = append(attrs, slog.Attr{
+					Key:   i,
+					Value: slog.StringValue(value[0]),
+				})
+			case len(value) > 1:
+				attrs = append(attrs, slog.Attr{
+					Key:   i,
+					Value: slog.AnyValue(value),
+				})
+			}
+		}
+
+		h.log.LogAttrs(
+			rWithCtx.Context(),
+			slog.LevelInfo,
+			"request called",
+			attrs...,
+		)
+
+		next.ServeHTTP(w, rWithCtx)
+
+		slog.Debug("request handled",
+			slog.String("request ID", reqID))
+	})
+}
+
+```
+
+## At the http Handler
+
+```go
+func HandleSomething(w http.ResponseWriter, r *http.Request) {
+	var (
+		ctx   context.Context = r.Context()
+		reqID string          = rctx.GetRequestID(ctx)
+		log   *slog.Logger    = slog.Default().With(
+            slog.String("req id", reqID),
+            slog.String("level", "handler"),
+        )
+	)
+
+    // do something and where is the case to log w/ req id:
+		log.Error("decode req body",
+			slog.String("error", err.Error()))
+    return
+}
+
+```