Update README.md to include ISO Codes for available languages

Wiki: https://en.wikipedia.org/wiki/Prakrit
Glottolog: https://glottolog.org/resource/languoid/id/maha1305

README.md

@@ -4,4 +4,7 @@ task_categories:
 - translation
 size_categories:
 - 1K<n<10K
+language:
+- en
+- pra
 ---