http/pprof: update readme (#138)

The readme for `http/pprof` doesn't compile currently: `Profile` is a `HandlerFunc`, not a `Handler`.

http/pprof/README.md

@@ -21,14 +21,16 @@ the `net/http/pprof` package is imported by dependencies, and therefore there is
 reliable way to avoid the conflict.
 
 ```go
+package main
+
 import (
     "net/http"
 
     "github.com/grafana/pyroscope-go/http/pprof"
 )
 
 func main() {
-	http.Handle("/debug/pprof/cpu", pprof.Profile())
+	http.HandleFunc("/debug/pprof/cpu", pprof.Profile)
 }
 ```