Clarify nucleus sample README

Author: waleedka

samples/nucleus/README.md

@@ -6,24 +6,24 @@ The `nucleus.py` file contains the main parts of the code, and the two Jupyter n
 
 
 ## Command line Usage
-Train a new model starting from ImageNet weights
+Train a new model starting from ImageNet weights using `train` dataset (which is `stage1_train` minus validation set)
 ```
 python3 nucleus.py train --dataset=/path/to/dataset --subset=train --weights=imagenet
 ```
 
-Train a new model starting from specific weights file
+Train a new model starting from specific weights file using the full `stage1_train` dataset
 ```
-python3 nucleus.py train --dataset=/path/to/dataset --subset=train --weights=/path/to/weights.h5
+python3 nucleus.py train --dataset=/path/to/dataset --subset=stage1_train --weights=/path/to/weights.h5
 ```
 
 Resume training a model that you had trained earlier
 ```
 python3 nucleus.py train --dataset=/path/to/dataset --subset=train --weights=last
 ```
 
-Generate submission file
+Generate submission file from `stage1_test` images
 ```
-python3 nucleus.py detect --dataset=/path/to/dataset --subset=train --weights=<last or /path/to/weights.h5>
+python3 nucleus.py detect --dataset=/path/to/dataset --subset=stage1_test --weights=<last or /path/to/weights.h5>
 ```