added usage of subtests and added descriptions for ocr-numbers

[eklatzer]

One of #2098

[github-actions]

Dear eklatzer

Thank you for contributing to the Go track on Exercism! 💙
You will see some automated feedback below 🤖. It would be great if you can make sure your PR covers those points. This will save your reviewer some time and your change can be merged quicker.

• ⬆️ The instructions and test cases for many practice exercises originate in the Exercism-wide problem-specifications repo. If the exercise you changed is listed there in the exercises folder, please consider the following.

  • Improvements to the instructions.md file should be made in the problem-spec repo so that all tracks can benefit.
    You can open a PR there instead.
  • If you want to add some language specific information, use the instructions.append.md file (see Practice Exercise Docs).
  • Test cases selected in the .meta/tests.toml file need to be implemented in the <exercise>_test.go file according to the specification in canonical-data.json.

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• 🔤 If your PR fixes an easy to identify typo, if would be great if you could check for that typo in the whole repo. For example, if you found Unicdoe, use "replace all" in your editor (or command line magic) to fix it consistently.

Dear Reviewer/Maintainer

• 📏 Make sure you set the appropriate x:rep label for the PR. (This also works after merging, in case you forgot about it.)

• 🔍 Don't be too nit-picky. If the PR is a clear improvement compared to the status quo, it should be approved as clear signal this is good to be merged even if the minor comments you might have are not addressed by the contributor. Further improvement ideas can be captured in issues (if important enough) and implemented via additional PRs.

• 🤔 After reviewing the diff in the "Files changed" section, take a moment to think about whether there are changes missing from the diff. Does something need to be adjusted in other places so the code or content stays consistent?

_{Automated comment created by PR Commenter 🤖.}

[andrerfcsantos]

Thanks!