net/url: fix docs for URL.String

Fixes #10227.

Change-Id: I64d5522e76da5a717e3c4169405e5ef35d6c262e
Signed-off-by: Shenghou Ma <minux@golang.org>
Reviewed-on: https://go-review.googlesource.com/7974
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/net/url/url.go b/src/net/url/url.go
index 737c95b..0ad68cc 100644
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -443,7 +443,7 @@
 // String reassembles the URL into a valid URL string.
 // The general form of the result is one of:
 //
-//	scheme:opaque
+//	scheme:opaque?query#fragment
 //	scheme://userinfo@host/path?query#fragment
 //
 // If u.Opaque is non-empty, String uses the first form;