read-cache: new API write_locked_index instead of write_index/write_cache

diff --git a/RelNotes b/RelNotes
index 00e77229ddadcb8a13b10b693a96bd76a4cb9f33..e50885caa1043665dfe2d995e0a2f7a7a7bb51ca 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.7.1.txt
\ No newline at end of file
+Documentation/RelNotes/2.0.0.txt
\ No newline at end of file