added a doc note

doc/tags/macro.rst

@@ -138,6 +138,12 @@ When calling ``import`` or ``from`` from a ``macro`` tag, the imported macros
 are only defined in the current macro and they override macros defined at the
 template level with the same names.
 
+.. note::
+
+    Before Twig 2.11, it was possible to use macros imported in a block in a
+    "sub-block". When upgrading to 2.11, you need to either move the import in
+    the global scope or reimport the macros explicitly in the "sub-blocks".
+
 Checking if a Macro is defined
 ------------------------------