Small update to DELF training README. (#8483)

* Merged commit includes the following changes:
253126424  by Andre Araujo:

    Scripts to compute metrics for Google Landmarks dataset.

    Also, a small fix to metric in retrieval case: avoids duplicate predicted images.

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253118971  by Andre Araujo:

    Metrics for Google Landmarks dataset.

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253106953  by Andre Araujo:

    Library to read files from Google Landmarks challenges.

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250700636  by Andre Araujo:

    Handle case of aggregation extraction with empty set of input features.

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250516819  by Andre Araujo:

    Add minimum size for DELF extractor.

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250435822  by Andre Araujo:

    Add max_image_size/min_image_size for open-source DELF proto / module.

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250414606  by Andre Araujo:

    Refactor extract_aggregation to allow reuse with different datasets.

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250356863  by Andre Araujo:

    Remove unnecessary cmd_args variable from boxes_and_features_extraction.

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249783379  by Andre Araujo:...

research/delf/delf/python/training/README.md

@@ -3,7 +3,7 @@
 ## Data preparation
 
 See the
-[build_image_dataset.py](https://github.com/andrefaraujo/models/blob/master/research/delf/delf/python/training/build_image_dataset.py)
+[build_image_dataset.py](https://github.com/tensorflow/models/blob/master/research/delf/delf/python/training/build_image_dataset.py)
 script to prepare the data, following the instructions therein to download the
 dataset (via Kaggle) and then running the script.