Documentation: describe %ifenv and friends

Signed-off-by: Bryant Keller <bkeller@assembly.ath.cx>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
diff --git a/doc/changes.src b/doc/changes.src
index 5e7bf06..e64aae7 100644
--- a/doc/changes.src
+++ b/doc/changes.src
@@ -9,6 +9,8 @@
 
 \S{cl-2.09} Version 2.09
 
+\b \c{%ifenv}, \c{%elifenv}, \c{%ifnenv}, and \c{%elifnenv} directives introduced.
+
 \b Fixed NULL dereference if environment variable is missed.
 
 \b Updates of new AVX v7 Intel instruciotns.