Update link to Sandboxing system services doc

The doc recently migrated to the ChromeOS Developer Library hosting.

BUG=None
TEST=Open in Markdown viewer

Change-Id: Icf77d76e3197daee95a542475cf46722c17c0239
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minijail/+/5387759
Auto-Submit: Ben Scarlato <akhna@google.com>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Tested-by: Ben Scarlato <akhna@google.com>
Commit-Queue: Jorge Lucangeli Obes <jorgelo@chromium.org>
diff --git a/README.md b/README.md
index 812895e..a33d4a9 100644
--- a/README.md
+++ b/README.md
@@ -98,7 +98,7 @@
 ## Example usage
 
 The ChromiumOS project has a comprehensive
-[sandboxing](https://chromium.googlesource.com/chromiumos/docs/+/HEAD/sandboxing.md)
+[sandboxing](https://www.chromium.org/chromium-os/developer-library/guides/development/sandboxing)
 document that is largely based on Minijail.
 
 After you play with the simple examples below, you should check that out.