DOC: Add TextureFeatures README pointing at upstream

Author: hjmjohnson

Modules/Filtering/TextureFeatures/README.md

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+# TextureFeatures
+
+In-tree ITK module providing N-dimensional textural feature image
+filters. The flagship classes compute first-order, run-length, and
+co-occurrence (GLCM) texture features over a sliding window for each
+voxel of an input image, producing per-feature output maps suitable
+for radiomics and computer-vision pipelines.
+
+The flagship filters are
+`itk::CoocurrenceTextureFeaturesImageFilter`,
+`itk::FirstOrderTextureFeaturesImageFilter`, and
+`itk::RunLengthTextureFeaturesImageFilter`, with supporting
+`itk::DigitizerFunctor` and `itk::FirstOrderTextureHistogram` building
+blocks.
+
+## Origin
+
+Ingested from the standalone remote module
+[**InsightSoftwareConsortium/ITKTextureFeatures**](https://github.com/InsightSoftwareConsortium/ITKTextureFeatures)
+on 2026-05-08, following the v4 ingestion guidelines defined in
+InsightSoftwareConsortium/ITK#6204. The upstream repository will be
+archived read-only after this PR merges; it remains reachable at the
+URL above for historical reference (notably the `doc/` and `example/`
+directories, which were intentionally left in the upstream archive).
+
+## References
+
+- Vimort J., McCormick M., Budin F., Paniagua B.
+  *Computing Textural Feature Maps for N-Dimensional images.*
+  The Insight Journal. January-December. 2017.
+  <https://doi.org/10.54294/qy48ty>