perf: update builder name, dashboard description

Change-Id: I1092207a01c5cf6c4d56f9900d33fba1317a1d12
Reviewed-on: https://go-review.googlesource.com/c/build/+/566975
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

perf/app/dashboard/index.html

@@ -80,9 +80,12 @@ license that can be found in the LICENSE file.
 	<p>
 		Note that some commits are not tested, so there could be
 		multiple commits (not shown) between two points on the graph.
-		See the <code>gotip-linux-amd64-perf_vs_release</code> column on the
-		<a href="https://ci.chromium.org/p/golang/g/go-gotip/console">build dashboard</a>
-		for tested ("ok") / untested (empty) commits.
+		See the <code>gotip-linux-amd64_debian12-perf_vs_release</code>
+		column on the
+		<a href="https://ci.chromium.org/p/golang/g/go-gotip/console">build dashboard</a>.
+		Individually tested commits have their own green box. A single
+		box that covers multiple commits indicates that only the latest
+		commit in the range was tested.
 	</p>
 	<p>
 		The 'Go branch' selection above is the Go branch that benchmarking