Update src/release-notes/sssd-2.9.9.rst

Co-authored-by: Alexey A Tikhonov <talex.pro@protonmail.com>

Author: pbrezina

src/release-notes/sssd-2.9.9.rst

@@ -15,8 +15,9 @@ General information
   Assurance (AMA).
 - Active Directory’s Foreign Security Principals (FSP) are now properly detected
   and ignored when reading nested group members. The
-  `ldap_ignore_unreadable_references` option is not needed anymore to ignore
-  FSPs only in cases where member objects are really not accessible.
+  ``ldap_ignore_unreadable_references`` option is only needed to ignore member
+  objects which are really not accessible.
+- A number of cache performance optimizations for large deployments.
 
 Tickets Fixed
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