Update 'README.md'

README.md

@@ -25,6 +25,22 @@ datalad clone https://gin.g-node.org/koch_means_cook/pedlr-derivatives.git
 For in integrated usage with the analysis described in the referenced preprint *(Koch, C., Zika, O., Bruckner, R., & Schuck, N. W. Influence of surprise on reinforcement learning in younger and older adults. https://doi.org/10.31234/osf.io/unx5y)* clone the Github code repository (doi:10.5281/zenodo.10211239), then clone this datalad repository into the code repository and rename the datalad repository folder to `derivatives`.
 This will allow the analysis scripts to directly use this dataset.
 
+Large files will not be downloaded automatically.
+To get them, you can use 
+
+```
+datalad get <filename>
+```
+
+Large files that have been downloaded will be 'locked' and therefore read-only.
+If you wish to write you will need to unlock them using
+
+```
+datalad unlock <filename>
+```
+
+For more information on locked/unlocked files see [here](https://handbook.datalad.org/en/latest/basics/101-114-txt2git.html).
+
 
 ## Data set structure