[dev.simd] simd: correct SumAbsDiff documentation

Change-Id: I6bb093615f12bbac5ea4c013a1c47cd5d338fe43
Reviewed-on: https://go-review.googlesource.com/c/go/+/698516
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: JunyangShao

src/simd/_gen/simdgen/ops/MLOps/categories.yaml

@@ -49,5 +49,5 @@
   commutative: false
   documentation: !string |-
     // NAME sums the absolute distance of the two input vectors, each adjacent 8 bytes as a group. The output sum will
-    // be a vector of word-sized elements whose each 8*n-th element contains the sum of the n-th input group.
+    // be a vector of word-sized elements whose each 4*n-th element contains the sum of the n-th input group. The other elements in the result vector are zeroed.
     // This method could be seen as the norm of the L1 distance of each adjacent 8-byte vector group of the two input vectors.