add .gitreview

A .gitreview file is required to use git review.
More information about git review
https://www.mediawiki.org/wiki/Gerrit/git-review

Change-Id: Ie7cdf16232181d4b8093e61f2d8a3faed9010d4f
diff --git a/.gitreview b/.gitreview
new file mode 100644
index 0000000..e7058f4
--- /dev/null
+++ b/.gitreview
@@ -0,0 +1,3 @@
+[gerrit]
+host=gerrit.osmocom.org
+project=sandbox