Add community Elixir implementation to README

[sloanelybutsurely]

hello! i've written an elixir implementation: https://github.com/sloanelybutsurely/typeid-elixir

the package is published on hex: https://hex.pm/packages/typeid_elixir and documentation is also on hexdocs: https://hexdocs.pm/typeid_elixir/TypeID.html

[loreto]

@sloanelybutsurely Thanks for contributing!

Three quick things:

1. Due to a quirk of our internal setup, I need to accept the PR in our opensource monorepo and then it'll automatically get published here. Do you mind opening the PR there? The corresponding file is here: https://github.com/jetpack-io/opensource/blob/main/typeid/typeid/README.md
2. I'm trying to keep the list in alphabetical order, so add the Elixir link after C#
3. If you want to mark your implementation as validated by the spec, I've added two files with test data: https://github.com/jetpack-io/typeid/blob/main/spec/valid.yml and https://github.com/jetpack-io/typeid/blob/main/spec/invalid.yml. If you can show your implementation has tests that pass using that data, I'll mark it as validated. This can happen later – we can go ahead and add your implementation to the list now and add the validation check mark once the tests are there.

[sloanelybutsurely]

@loreto okay good deal! i'll use this test data to validate my implementation against the spec and open a new PR over there :+1:

[sloanelybutsurely]

discussion moved to jetpack-io/opensource