add SIMD changes

CHANGES.SIMD.rst

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+Changelog (Pillow-SIMD)
+=======================
+
+3.3.0.post0
+-----------
+
+Resampling
+~~~~~~~~~~
+
+- SSE4 and AVX2 fixed-point full loading horizontal pass.
+- SSE4 and AVX2 fixed-point full loading vertical pass.
+
+Convertion
+~~~~~~~~~~
+
+- RGBA -> RGBa SSE4 and AVX2 fixed-point full loading implementations.
+  Up to 2.6x faster.
+- RGBa -> RGBA AVX2 implementation using gather instructions.
+  Up to 5x faster.
+
+Alpha composite
+~~~~~~~~~~~~~~~
+
+- SSE4 and AVX2 implementations. Up to 4.3x faster.
+
+
+3.2.0.post3
+-----------
+
+Resampling
+~~~~~~~~~~
+
+- SSE4 and AVX2 float full loading horizontal pass.
+- SSE4 float full loading vertical pass.
+
+
+3.2.0.post2
+-----------
+
+Resampling
+~~~~~~~~~~
+
+- SSE4 and AVX2 float full loading horizontal pass.
+- SSE4 float per-pixel loading vertical pass.
+
+
+2.9.0.post1
+-----------
+
+Resampling
+~~~~~~~~~~
+
+- SSE4 and AVX2 float per-pixel loading horizontal pass.
+- SSE4 float per-pixel loading vertical pass.
+- SSE4: Up to 2x for downscaling. Up to 3.5x for upscaling.
+- AVX2: Up to 2.7x for downscaling. Up to 3.5x for upscaling.
+
+
+Box blur
+~~~~~~~~
+
+- Simple SSE4 fixed-point implementations with per-pixel loading.
+- Up to 2.1x faster.