Add changelog entry for ocaml#1076

Signed-off-by: Paul-Elliot <peada@free.fr>

Author: panglesd

CHANGES.md

@@ -19,6 +19,9 @@
 - Add a marshalled search index consumable by sherlodoc (@EmileTrotignon, @panglesd, #1084)
 - Add a `--index` argument to pass indexes to the document generation, currently
   used for sidebar (@panglesd, #1145)
+- Added a `--occurrences` argument to the `compile-index` command to output the
+  number of occurrences of each entry of the index in the json output
+  (@panglesd, #1076).
 
 ### Changed