Add changelog entry for #281

Author: akashchamp

doc/source/whatsnew.rst

@@ -11,8 +11,14 @@ v2.2.0.dev0
   (`#265`_).
 * The C source generated by ``cffi-gen-src`` and ``ffibuilder.emit_c_code()``
   no longer depends on the interpreter running the generator.
+* ``cdef()`` now raises a clean ``CDefError`` instead of crashing the whole
+  process with a fatal error when given an explicit definition of
+  ``struct _IO_FILE``, the name cffi uses internally for the opaque
+  ``FILE`` type. This could happen with an already-preprocessed system
+  header, which spells out the real struct. (`#281`_).
 
 .. _`#265`: https://github.com/python-cffi/cffi/pull/265
+.. _`#281`: https://github.com/python-cffi/cffi/pull/281
 
 v2.1.0
 ======