playground: link to the playground source code in the help page

Fixes golang/go#23658

Change-Id: I68b68497af0a39c1026bfb320d774183ae627801
Reviewed-by: Andrew Bonventre <>
diff --git a/edit.html b/edit.html
index 0be1443..826e4fb 100644
--- a/edit.html
+++ b/edit.html
@@ -164,8 +164,10 @@
-The article "<a href="" target="_blank">Inside
+The article "<a href="" target="_blank" rel="noopener">Inside
 the Go Playground</a>" describes how the playground is implemented.
+The source code is available at <a href="" target="_blank" rel="noopener">