updating readme with some details

README.md

@@ -1,4 +1,58 @@
 harhar
 ======
 
-Simple Transparent HAR logging for server-side Go http.Client usage.
+Simple, transparent HAR logging for Go code using the http.Client interface.
+For existing code that already uses the `net/http` package, updating it to
+produce HAR logs is typically only 2 lines of code.
+
+Getting Started
+---------------
+
+First, convert your existing http.Client instance (or http.DefaultClient) to
+a harhar.Client:
+
+	// before
+    webClient := &http.Client{}
+
+    // after
+    httpClient := &http.Client{}
+    webClient := harhar.NewClient(httpClient)
+
+Then, whenever you're ready to generate the HAR output, call WriteLog:
+
+	webClient.WriteLog("output.har")
+
+That's it! harhar.Client implements all the same methods as http.Client, so no
+other code will need to be changed. However, if you set Timeouts, Cookies, etc.
+dynamically then you will want to retain a copy of the wrapped http.Client.
+harhar.Client only stores the pointer, so changes to the underlying http.Client
+will be used immediately.
+
+Optional periodic logging
+-------------------------
+
+To dynamically enable or disable HAR logging, code can use harhar.ClientInterface
+to represent either an http.Client or harhar.Client. When using this interface,
+you can write logs (if enabled) by using this simple block of code:
+
+	if harCli, ok := myClient.(*harhar.Client); ok {
+		harCli.WriteLog("output.har")
+	}
+
+When combined with a long-running process, the interface makes it possible to
+toggle logging off and on, and periodically write to disk throughout a processes
+lifetime. An example is the following (never-ending) goroutine:
+
+	go func(){
+		for _ = range time.Tick(time.Minute*5) {
+			if harCli, ok := myClient.(*harhar.Client); ok {
+				sz, err := harCli.WriteLog("output.har")
+				if err!=nil {
+					log.Println("error writing .har log:", err)
+				} else {
+					log.Printf("wrote .har log (%.1fkb)\n", float64(sz)/1024.0)
+				}
+			}
+		}
+	}()
+