Add .arcconfig so code review are automatically associated with the right

repository and to prevent people using git svn/hg svn to have arcanist
automatically modifying their history

Approved by:	gjb

.arcconfig

@@ -0,0 +1,5 @@
+{
+	"project.name": "D",
+	"phabricator.uri" : "https://phabric.freebsd.org/",
+	"history.immutable" : true
+}