Document the behavior change of make apidoc
diff --git a/ChangeLog b/ChangeLog
index 61a0631..5d2bb47 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -27,6 +27,11 @@
    * Fix potential build failures related to the 'apidoc' target, introduced
      in the previous patch release. Found by Robert Scheck. #390 #391
 
+Changes
+   * "make apidoc" now generates the documentation for the current
+     configuration. Run "scripts/apidoc_full.sh" to generate the full
+     documentation. This aligns the behavior with Mbed TLS 2.2+.
+
 = mbed TLS 2.1.14 branch released 2018-07-25
 
 Security