Add approportionment.

README.md

@@ -80,6 +80,7 @@ A curated list of awesome dhall-lang binding, libraries and anything related to
 - [cpkg](https://github.com/vmchale/cpkg) - A build tool/package manager for C, configured with Dhall.
 - [updo](https://github.com/cabalism/updo) - From Dhall configuration, generate Stack and Cabal projects with Dhall text templating.
 - [dhall-mock](https://github.com/dhall-mock/dhall-mock) - A HTTP mock server based on Dhall configuration.
+- [approportionment](https://github.com/akazukin5151/approportionment) - Yee diagrams generator for multi-winner electoral methods designed for proportional representation, configured with Dhall.
 
 ## Text Editor Support
 - [dhall-vim](https://github.com/vmchale/dhall-vim) - Syntax highlighting in Vim for Dhall.