Print ACME account URL on client creation

Fixes issue #9.

acme.go

@@ -132,8 +132,9 @@ func (a *ACME) acmeClient(ctx context.Context) (*acme.Client, error) {
 	// Register the account (accept TOS) if necessary. If the
 	// account is already registered we get a StatusConflict,
 	// which we can ignore.
-	_, err = client.Register(ctx, ac, func(_ string) bool { return true })
+	acct, err := client.Register(ctx, ac, func(_ string) bool { return true })
 	if ae, ok := err.(*acme.Error); err == nil || err == acme.ErrAccountAlreadyExists || (ok && ae.StatusCode == http.StatusConflict) {
+		log.Printf("ACME account %s", acct.URI)
 		a.client = client
 		err = nil
 	}