doc: Document elfx32 support

Document the new elfx32 backend.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/doc/changes.src b/doc/changes.src
index ab6fb52..d6a9977 100644
--- a/doc/changes.src
+++ b/doc/changes.src
@@ -42,6 +42,9 @@
 
 \b Add support for Intel Transactional Synchronization Extensions (TSX).
 
+\b Add support for x32 ELF (32-bit ELF with the CPU in 64-bit mode.)
+   See \k{elffmt}.
+
 \S{cl-2.09.10} Version 2.09.10
 
 \b Fix up NSIS script to protect uninstaller against registry keys
@@ -49,7 +52,6 @@
    to a user during deinstallation procedure but still it is better
    than unpredictable file removal.
 
-
 \S{cl-2.09.09} Version 2.09.09
 
 \b Fix initialization of section attributes of \c{bin} output format.