Add changelog entry

Signed-off-by: gufe44 <gu981@protonmail.com>
diff --git a/ChangeLog.d/netbsd-rand-arc4random_buf.txt b/ChangeLog.d/netbsd-rand-arc4random_buf.txt
new file mode 100644
index 0000000..7f5802e
--- /dev/null
+++ b/ChangeLog.d/netbsd-rand-arc4random_buf.txt
@@ -0,0 +1,3 @@
+Changes
+   * Use arc4random_buf on NetBSD instead of rand implementation with cyclical
+     lower bits. Fix contributed in #3540.