Small edits to DELF markdown instructions (#6839)

* Initial feature aggregation code for Detect-to-Retrieve paper.

PiperOrigin-RevId: 246043144

* Add support for ASMK/ASMK*/R-ASMK/R-ASMK*.

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* Add DatumProto uint32 field, and limit datum_io to uint32 and float32/float64 types.

Also, introduce DatumPairProto, to be used for ASMK variants. Functions to read/write in this new format are added and tested.

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* Add batching option to feature aggregation extraction.

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* Script to perform local feature aggregation, with associated configs.

Also small edits to the aggregation extractor, for better handling of input features / avoiding OOM.

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* Tests to check that aggregation using regions with no local features works.

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* Include new library/proto for aggregation

* Merged commit includes the following changes:

PiperOrigin-RevId: 248176511

* Merged commit includes the following changes:
248194572  by Andre Araujo:

    Change tf.tensor_scatter_nd_add --> tf.compat.v1.tensor_scatter_add to make it compatible with TF 1.X.

--

PiperOrigin-RevId: 248194572

* Functions to parse ground-truth and compute metrics for revisited datasets.

Unit tests are added.

PiperOrigin-RevId: 248561575

* Small change to argparse bool option, which does not work as expected.

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* Class to compute similarity between aggregated descriptors.

PiperOrigin-RevId: 249102986

* Script to perform retrieval and compute metrics.

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* feature_aggregation_similarity library in DELF init

* D2R instructions / README update

* Small edit to README

* Internal change.

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* Instructions to reproduce D2R paper results, and small edits to config files.

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* Revert "Internal change."

This reverts commit 0529f2b8471a20c88f1fbb37367f142965d098ee.

Undoing incorrect markdown deletion.

* Small updates to markdown instructions

* Small updates to markdown instructions 2

research/delf/DETECTION.md

 ## Quick start: landmark detection
 
+### Install DELF library
+
+To be able to use this code, please follow
+[these instructions](INSTALL_INSTRUCTIONS.md) to properly install the DELF
+library.
+
 ### Download Oxford buildings dataset
 
 To illustrate detector usage, please download the Oxford buildings dataset, by

research/delf/EXTRACTION_MATCHING.md

 ## Quick start: DELF extraction and matching
 
+### Install DELF library
+
+To be able to use this code, please follow
+[these instructions](INSTALL_INSTRUCTIONS.md) to properly install the DELF
+library.
+
 ### Download Oxford buildings dataset
 
 To illustrate DELF usage, please download the Oxford buildings dataset. To

research/delf/delf/python/detect_to_retrieve/DETECT_TO_RETRIEVE_INSTRUCTIONS.md

@@ -4,6 +4,12 @@ These instructions can be used to reproduce the results from the
 [Detect-to-Retrieve paper](https://arxiv.org/abs/1812.01584) for the Revisited
 Oxford/Paris datasets.
 
+### Install DELF library
+
+To be able to use this code, please follow
+[these instructions](../../../INSTALL_INSTRUCTIONS.md) to properly install the
+DELF library.
+
 ### Download datasets
 
 ```bash