add .gitreview to support git review plugin

Change-Id: Ia197da1614a8cbec5f177368ca9e25946059c68a
diff --git a/.gitreview b/.gitreview
new file mode 100644
index 0000000..972358d
--- /dev/null
+++ b/.gitreview
@@ -0,0 +1,3 @@
+[gerrit]
+host=gerrit.osmocom.org
+project=libasn1c