Fix usage part in README

README.md

@@ -81,11 +81,21 @@ First, from the command line install the `datasets` library
 
     $ pip install datasets
 
-then, from within python load the datasets library
+then, from within python load the datasets library.
 
-    >>> import datasets
+    >>> from datasets import load_dataset, Features, Value
 
-and load one of the 'ChAFF' datasets, e.g.,
+Specifiy column types to prevent pyarrow error.
+    >>> features = Features({
+    "Type": Value("string"),
+    "DatasetName": Value("string"),
+    "AID": Value("int64"),     
+    "ID": Value("string"),
+    "IDType": Value("string"),
+    "SMILES": Value("string")
+})
+
+Now load one of the 'ChAFF' datasets, e.g.,
 
     >>> dataset = datasets.load_dataset("maomlab/ChAFF", name = "default", data_files = "data/Absorbance.csv", split="train")