documentation: add Bengali as a language in active development (#289)

Added Bengali as a language in active development to the README file.
- thank you @SandipPalit for your contribution! 🎉

README.md

@@ -68,6 +68,7 @@ We are actively working on adding as many written languages as we can for versio
 - [Afar (aa)](https://github.com/legesher/legesher-translations/issues?q=label%3A"Dialect%3A+Afar")
 - [Arabic (ar)](https://github.com/legesher/legesher-translations/issues?q=label%3A"Dialect%3A+Arabic")
 - [Azerbaijani (az)](https://github.com/legesher/legesher-translations/issues?q=label%3A"Dialect%3A+Azerbaijani")
+- [Bengali (bn)](https://github.com/legesher/legesher-translations/issues?q=label%3A"Dialect%3A+Bengali")
 - [Danish (da)](https://github.com/legesher/legesher-translations/issues?q=label%3A"Dialect%3A+Danish")
 - [Dutch (nl)](https://github.com/legesher/legesher-translations/issues?q=label%3A"Dialect%3A+Dutch")
 - [Finnish (fi)](https://github.com/legesher/legesher-translations/issues?q=label%3A"Dialect%3A+Finnish")