Set the target branch for `arc land` to main
diff --git a/.arcconfig b/.arcconfig
index 9cb8880..412ead9 100644
--- a/.arcconfig
+++ b/.arcconfig
@@ -2,5 +2,6 @@
   "phabricator.uri" : "https://reviews.llvm.org/",
   "repository.callsign" : "G",
   "conduit_uri" : "https://reviews.llvm.org/",
-  "base": "git:HEAD^"
+  "base": "git:HEAD^",
+  "arc.land.onto.default": "main"
 }