From its README:
rg --type-add 'foo:*.{foo,foobar}' -tfoo bar
---
You simply make the below into an alias:
rg --type-add 'foo:*.{foo,foobar}'
Or, if the type you need is generic that other users can also use, submit a PR. The developer was kind to except mine..
https://github.com/BurntSushi/ripgrep/pull/107/files .. it's a trivial 1-line PR.