RELNOTES: add private-lib modif

Added on commit b689b69 ("make --private-lib a compile time option,
disabled by default", 2023-03-09) and on commit 91f2b3f ("private-lib
cleanup", 2023-03-09).

Relates to #5727 #5732.

RELNOTES

@@ -12,6 +12,8 @@ firejail (0.9.73) baseline; urgency=low
   * modif: Allow mostly only ASCII letters and digits for sandbox name
     (--name=) and host name (--hostname=) (#5708 #5856)
   * modif: remove firemon --interface option (duplicating --net.print option)
+  * modif: make private-lib a configure-time option, disabled by default (see
+    --enable-private-lib) (#5727 #5732)
   * modif: Improve --version/--help & print version on startup (#5829)
   * bugfix: qutebrowser: links will not open in the existing instance (#5601
     #5618)