docs: some small notes on neural networks needing the .nn file extens…

…ion in order to saved correctly with git-lfs.

docs/brage.md

@@ -3,3 +3,9 @@
 [Brage project](https://github.com/BrageHK/IDATT2502-prosjekt/tree/main)
 
 [openspiel documentation](https://openspiel.readthedocs.io/en/latest/api_reference.html)
+
+## Neural network models
+
+Models should be saved with the .nn file extension.
+This prompts git to save the models using git lfs, which if not used,
+will make the repository size impractically large.