codereview.cfg: add

So the codereview tool can recognize issue references and rewrite
to golang/go#NNN.

Change-Id: I3e9110e6d473b281bad2300e45587fe65cbe0c67
Reviewed-on: https://go-review.googlesource.com/c/telemetry/+/711361
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

codereview.cfg

diff --git a/codereview.cfg b/codereview.cfg
new file mode 100644
index 0000000..3f8b14b
--- /dev/null
+++ b/codereview.cfg
@@ -0,0 +1 @@
+issuerepo: golang/go