Add training data for HEA.

mvl_models/pes/MoNbTaW/training/README.md

@@ -0,0 +1,24 @@
+# Using the training and test data
+
+The training and test data is provided in json files, which can be read by any standard json parser. Each json file contains one data group (e.g., Ta_Surface, NbMo_SS, Multinary_SQS,Mo_Test,NbMo_Test, etc.) used in the training or test of the SNAP model.
+
+The data is provided as a list of dicts. Each dict contains one structure with data. The format of the json file is as follows:
+
+```json
+[
+    {
+        "_id": "a string",
+        "params": {"Dict of parameters used for DFT calculations, e.g. pseudopotential, energy cutoff, etc."},
+        "group": "Ni3Mo",
+        "tags": "Md",
+        "structure": {"Dict representation of Structure as output by pymatgen"},
+        "num_atoms": 108,
+        "outputs": {
+            "energy": -619.08666252,
+            "forces": [],
+            "stress": []
+        }
+    },
+    ...
+]
+```