Add buildbucket.config

Bug: chromium:773436
diff --git a/buildbucket.config b/buildbucket.config
new file mode 100644
index 0000000..bb28552
--- /dev/null
+++ b/buildbucket.config
@@ -0,0 +1,3 @@
+[host]
+	git = boringssl.googlesource.com
+	gerrit = boringssl-review.googlesource.com