read-cache: use shared perms when writing shared index

diff --git a/RelNotes b/RelNotes
index cdb1b4853d82672422f455f022015014741ffecd..d75ac9dd09072809084680945aef73c86c20fa3a 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/2.5.4.txt
\ No newline at end of file
+Documentation/RelNotes/2.13.2.txt
\ No newline at end of file