exp: add codereview.cfg

Change-Id: I0208527b823d0a6217906dac3fefbd20979fdfd8
diff --git a/codereview.cfg b/codereview.cfg
new file mode 100644
index 0000000..e67a9bc
--- /dev/null
+++ b/codereview.cfg
@@ -0,0 +1 @@
+issuerepo: upspin/upspin