Add a healthcheck endpoint (#48)

Signed-off-by: Quentin Gliech <quenting@element.io>

changelog.d/48.misc

@@ -0,0 +1 @@
+Add a /health endpoint that always replies with a 200 OK.

main.go

@@ -167,6 +167,10 @@ func main() {
 	}
 	http.Handle("/api/listing/", fs)
 
+	http.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, "ok")
+	})
+
 	log.Println("Listening on", *bindAddr)
 
 	log.Fatal(http.ListenAndServe(*bindAddr, nil))