Update call for contributions

call_for_contributions.md

@@ -48,3 +48,27 @@ Recommendations:
 ## Learning to rank
 
 [Reference Kaggle competition](https://www.kaggle.com/c/wm-2017-learning-to-rank)
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+## Large-scale multi-label text classification
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+Using word bi-grams + TF-IDF + a small MLP, from raw text strings.
+The tokenization and extraction of TF-IDF ngrams should be done with the `TextVectorization` layer.
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+The dataset should have at least 50k samples and there should be at least a dozen of labels.
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+## DETR: End-to-End Object Detection with Transformers
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+[Reference implementation](https://github.com/facebookresearch/detr)
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+
+## 3D image classification
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+Using a dataset of CT scans (a few are available on Kaggle).
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+The model should use `Conv3D` layers.
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