Add summary for rpm 4.20 API changes

wiki/Releases/4.20.0.md

@@ -72,6 +72,17 @@ Last update: 2024-09-10
 * Python API examples are now provided and installed into `${CMAKE_INSTALL_DOCDIR}`
 * Lua API has a new `rpm.spawn()` function that supersedes `rpm.execute()` and provides more fine-grained control, currently for redirecting stdin, stdout and stderr to given paths ([#3192](https://github.com/rpm-software-management/rpm/issues/3192))
 
+### API changes
+* Added rpmdsIsSysuser() for determining sysusers-dependencies
+* Added rpmPushMacroAux(), rpmMacroEntryPriv(), rpmMacroBufAppend(),
+  rpmMacroBufAppendStr() and rpmMacroBufErr() to support auxiliary macros
+  implemented in C
+* Added rpmPluginName(), rpmPluginOpts(), rpmPluginSetData(), rpmPluginGetData()
+  and various type definitions and other symbols to support rpm plugin creation
+  (details in rpmplugin.h)
+* Added new tag format symbol RPMTD_FORMAT_JSON
+* Removed several unused type and struct definitions related to the OpenPGP standard (details in rpmpgp.h)
+
 ## Internal Cleanup
 * The internal OpenPGP parser has been removed.  RPM can now also be built completely without OpenPGP support (i.e. without Sequoia) to allow for easier bootstrapping, see the INSTALL file for details. ([#2414](https://github.com/rpm-software-management/rpm/issues/2414))
 * The Python bindings have been ported to the stable Python ABI ([#2345](https://github.com/rpm-software-management/rpm/issues/2345))