Add placeholder 2.2 release notes file

doc/release-notes-v2-2.rst

@@ -0,0 +1,21 @@
+=========================
+Duktape 2.2 release notes
+=========================
+
+Release overview
+================
+
+Main changes in this release (see RELEASES.rst for full details):
+
+* TBD.
+
+Upgrading from Duktape 2.0
+==========================
+
+No action (other than recompiling) should be needed for most users to upgrade
+from Duktape v2.1.x.  Note the following:
+
+* Call stack (including both activation records and catcher records) is no
+  longer a resized monolithic allocation which improves memory behavior for
+  very low memory targets.  If you're using a pool allocator, you may need to
+  measure and adjust pool sizes/counts.