Add changelog entry for #3208: md.c switch case unification

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/ChangeLog.d/md_switch.txt b/ChangeLog.d/md_switch.txt
new file mode 100644
index 0000000..a4d369b
--- /dev/null
+++ b/ChangeLog.d/md_switch.txt
@@ -0,0 +1,3 @@
+Changes
+   * Combine identical cases in switch statements in md.c. Contributed
+     by irwir in #3208.