README with run results

pdq/cpp/hashing/README.md

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+# Benchmark for hashing
+Benchmark for PDQ hashing on images
+
+## Instructions
+```
+cd pdq/cpp
+make bin/benchmark-photo-hasher
+./benchmark-photo-hasher
+```
+
+Help command:
+```
+$ ./benchmark-query -h
+Usage: ./benchmark-photo-hasher [options] folder_path
+Options:
+  -v               Verbose output
+  -n N             Total number of hashes to generate, can be more or less than the number of images in the folder
+                           (default: 0, meaning generate one hash for each image in the folder)
+  --dihedral       Compute dihedral versions of the hashes (default: false)
+```
+
+Note: if `-n N` is larger than the number of images in the folder, the benchmark will loop over each image in the folder until `N` hashes have been generated
+
+## Results
+Ran on Ubuntu 24.04.1 LTS, Intel Core i7-14700KF with 20 cores, 28 threads, 64GB RAM
+
+```
+$ ./benchmark-photo-hasher ../data/reg-test-input/dih/
+PHOTO COUNT:               8
+ERROR COUNT:               0
+TIME SPENT HASHING PHOTOS (SECONDS):     0.015171
+PHOTOS HASHED PER SECOND:   527.324158
+TIME SPENT READING PHOTOS (SECONDS):        0.299410
+PHOTOS READ PER SECOND:     26.719229
+
+$ ./benchmark-photo-hasher -n 10 ../data/reg-test-input/dih/
+PHOTO COUNT:               10
+ERROR COUNT:               0
+TIME SPENT HASHING PHOTOS (SECONDS):     0.018181
+PHOTOS HASHED PER SECOND:   550.028442
+TIME SPENT READING PHOTOS (SECONDS):        0.334852
+PHOTOS READ PER SECOND:     29.863914
+
+$ ./benchmark-photo-hasher -n 100 ../data/reg-test-input/dih/
+PHOTO COUNT:               100
+ERROR COUNT:               0
+TIME SPENT HASHING PHOTOS (SECONDS):     0.182545
+PHOTOS HASHED PER SECOND:   547.810364
+TIME SPENT READING PHOTOS (SECONDS):        2.841218
+PHOTOS READ PER SECOND:     35.196167
+
+$ ./benchmark-photo-hasher -n 1000 ../data/reg-test-input/dih/
+PHOTO COUNT:               1000
+ERROR COUNT:               0
+TIME SPENT HASHING PHOTOS (SECONDS):     1.767847
+PHOTOS HASHED PER SECOND:   565.659729
+TIME SPENT READING PHOTOS (SECONDS):        27.135609
+PHOTOS READ PER SECOND:     36.851948
+```