Add changelog

Signed-off-by: Ryan Everett <ryan.everett@arm.com>
diff --git a/ChangeLog.d/fix-concurrently-loading-non-existent-keys.txt b/ChangeLog.d/fix-concurrently-loading-non-existent-keys.txt
new file mode 100644
index 0000000..8a406a1
--- /dev/null
+++ b/ChangeLog.d/fix-concurrently-loading-non-existent-keys.txt
@@ -0,0 +1,4 @@
+Bugfix
+   * Fix rare concurrent access bug where attempting to operate on a
+     non-existent key while concurrently creating a new key could potentially
+     corrupt the key store.