doc: Update Ada User Guide to match C

doc/ada_user/ada_user.texi

@@ -112,6 +112,7 @@
 * CPU Usage Statistics::
 * Object Services::
 * Chains::
+* Red-Black Trees::
 * Timespec Helpers::
 * Constant Bandwidth Server Scheduler API::
 * Directive Status Codes::
@@ -156,6 +157,7 @@
 @include user/cpuuse.texi
 @include user/object.texi
 @include user/chains.texi
+@include user/rbtree.texi
 @include user/timespec.texi
 @include user/cbs.texi
 @include user/dirstat.texi