make GitHub recognise that this repo contains mostly JSON, not JS

[k-yle]

GitHub currently shows this repo as "100% JavaScript", which is a bit misleading, because this repo is actually a collection of a JSON files, with a tiny number of JS build scripts.

We can instruct the 'linguist' library to count JSON as source code.

Before	After

To test: open k-yle/id-tagging-schema, where I changed the default branch to this PR's branch.

[github-actions]

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Please use this preview to check your changes. Ideally use the test documentation template and document your test results by commenting on the PR. This will speed up the review process for everyone.

FYI, once this PR is merged, you can use the iD Editor Preview to test your changes in interaction with all other changes.

[matkoniecz]

Is it some official git syntax or some proprietary kludge?

From rereading docs it seems fine to put random stuff there. And I guess that it is not like this one is causing noticeable vendor lock-in.

[tyrasd]

Neat, thanks!

[k-yle]

Is it some official git syntax or some proprietary kludge?

Sorry I missed your comment, but GitHub, GitLab, Gitea, and Codeberg all recognise these attributes now, so it's a fairly established standard