Update README.md

benchs/bench_all_ivf/README.md

+# Benchmark of IVF variants
 
+This is a benchmark of IVF index variants, looking at compression vs. speed vs. accuracy. 
+The results are in [this wiki chapter](https://github.com/facebookresearch/faiss/wiki/Indexing-1G-vectors)
+
+
+The code is organized as: 
+
+- `datasets.py`: code to access the datafiles, compute the ground-truth and report accuracies
+
+- `bench_all_ivf.py`: evaluate one type of inverted file
+
+- `run_on_cluster_generic.bash`: call `bench_all_ivf.py` for all tested types of indices. 
+Since the number of experiments is quite large the script is structued so that the benchmark can be run on a cluster.
+
+- `parse_bench_all_ivf.py`: make nice tradeoff plots from all the results. 
+
+The code depends on Faiss and can use 1 to 8 GPUs to do the k-means clustering for large vocabularies. 
+
+It was run in October 2018 for the results in the wiki.