Add .gitupstream file

Change-Id: I4506226c530f5f84add3e5addfc14bcd43bf1f2a
diff --git a/.gitupstream b/.gitupstream
new file mode 100644
index 0000000..4bb08c4
--- /dev/null
+++ b/.gitupstream
@@ -0,0 +1 @@
+https://android.googlesource.com/platform/packages/apps/Launcher3