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: I95235dddf60670c38a5a7a726c2a77f09d03c303
Reviewed-on: https://gerrit.osmocom.org/69
Tested-by: Jenkins Builder
Reviewed-by: Holger Freyther <holger@freyther.de>

.gitreview

@@ -0,0 +1,3 @@
+[gerrit]
+host=gerrit.osmocom.org
+project=libosmocore