Added instructions for testing from command line

README.md

 # Instant Neural Graphics Primitives - for Tomography ![](https://github.com/NVlabs/instant-ngp/workflows/CI/badge.svg)
 
+Generate a save point (35000 steps by default, takes a few minutes):
+``` sh
+python ./scripts/run.py --training_data ../path/to/data/transforms.json --save_snapshot ../data/shepp-50-35000.ingp [--n_steps 20000]
+```
+
+Visualise it in the gui:
+```sh
+python ./scripts/run.py --load_snapshot ../data/shepp-50-35000.ingp --gui
+```
+
+Test it on unseen data (gives a PSNR - peak signal noise ratio).  Only the first image in the test dataset will be generated and compared to the ground truth
+```sh
+python ./scripts/run.py --load_snapshot ../data/shepp-50-35000.ingp --test_transforms ../data/shepp_test/transforms.json --screenshot_dir ../data
+```
+
+
 <img src="docs/assets_readme/fox.gif" height="342"/> <img src="docs/assets_readme/robot5.gif" height="342"/>
 
 Ever wanted to train a NeRF model of a fox in under 5 seconds? Or fly around a scene captured from photos of a factory robot? Of course you have!