Add nltk and sentencepiece to requirements

requirements.txt

@@ -5,10 +5,12 @@ editdistance==0.6.2
 imageio==2.26.1
 imagesize==1.4.1
 mdutils==1.6.0
+nltk==3.8.1
 numpy==1.24.3
 prettytable==3.8.0
 PyYAML==6.0
 scipy==1.10.1
+sentencepiece==0.1.99
 teklia-line-image-extractor==0.2.8rc4
 tenacity==8.2.3
 tensorboard==2.12.2