git-review: add config file

This is used by the `git review` tool that some people use.

Change-Id: I8dac4e1dad155109a05181deaec61e1a74857b1f
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/323698
Reviewed-by: Raman Tenneti <rtenneti@google.com>
Tested-by: Mike Frysinger <vapier@google.com>
diff --git a/.gitreview b/.gitreview
new file mode 100644
index 0000000..35a13c0
--- /dev/null
+++ b/.gitreview
@@ -0,0 +1,5 @@
+[gerrit]
+host=gerrit-review.googlesource.com
+scheme=https
+project=git-repo.git
+defaultbranch=main