Add a simple .arcconfig to make using the 'arc' commandline tool and the

phabricator code review site easier with libc++.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@171275 91177308-0d34-0410-b5e6-96231b3b80d8

.arcconfig

@@ -0,0 +1,4 @@
+{
+  "project_id" : "libcxx",
+  "conduit_uri" : "http://llvm-reviews.chandlerc.com/"
+}