Update package description for generated source.properties

Bug: 28042274
Change-Id: I8f420a828b97b6c94be2d4041b3eaff07df514a8
diff --git a/build.gradle b/build.gradle
index 9aa0557..0f18ae5 100644
--- a/build.gradle
+++ b/build.gradle
@@ -114,6 +114,7 @@
 Archive.Arch=ANY\n\
 Extra.NameDisplay=Android Support Repository\n\
 Archive.Os=ANY\n\
+Pkg.Desc=Local Maven repository for Support Libraries\n\
 Pkg.Revision=${project.ext.extraVersion}.0.0\n\
 Extra.VendorId=android"