Add description

ssj500k.py

@@ -20,7 +20,12 @@ import datasets
 
 
 _CITATION = ''
-_DESCRIPTION = """
+_DESCRIPTION = """The dataset contains 7432 training samples, 1164 validation samples and 893 test samples. 
+Each sample represents a sentence and includes the following features: sentence ID ('sent_id'), 
+list of tokens ('tokens'), list of lemmas ('lemmas'), 
+list of Multext-East tags ('xpos_tags), list of UPOS tags ('upos_tags'), list of morphological features ('feats'), 
+list of IOB tags ('iob_tags'), and list of universal dependency tags ('uds'). Three dataset configurations are
+available, where the corresponding features are encoded as class labels: 'ner', 'upos', and 'ud'.
 """
 _HOMEPAGE = ''
 _LICENSE = ''