_content: add blog link to go.dev/rebuild

Change-Id: I083c0753c43020c5d3a03818893ef203afa77652
Reviewed-on: https://go-review.googlesource.com/c/website/+/524395
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

_content/rebuild.html

@@ -14,6 +14,8 @@ pre { margin-left: 2em; }
 As of Go 1.21, Go's binary toolchain downloads served by <a href="/dl/">go.dev/dl/</a> can be
 reproduced and verified by anyone, on any platform,
 using <a href="https://pkg.go.dev/golang.org/x/build/cmd/gorebuild">golang.org/x/build/cmd/gorebuild</a>.
+For more details, see the blog post
+“[Perfectly Reproducible, Verified Go Toolchains](/blog/rebuild).”
 </p>
 
 <p>