Created arithmetic operators concept, as per #1049

[JaPrad]

Part of #1049

[junedev]

Well done overall, thanks a lot! I left some ideas for improvements. I mostly commented on the about.md file but if you fix something there, it might also need to be fixed in the introduction file.

[JaPrad]

Thank you for reviewing @junedev. I've incorporated your improvement suggestions.

[junedev]

@JaPatGitHub Thanks for the update! I made some more minor adjustments here b69cb1c.

Some general points to be aware of going forward:

• We use a special system for links called "reference links" where you write the actual link at the bottom (see https://exercism.org/docs/building/markdown/markdown for details).
• The link text should ideally be something meaningful, so instead of read more about this [here], use something like read more about this in the [MDN article on xyz].
• If you don't want to re-assign something, use const in the code examples.
• To pass the CI checks, the code needs to be formatted in a certain way, how to do the formatting is described here: https://github.com/exercism/javascript/blob/main/CONTRIBUTING.md#format

I also added your new content to the exercise introduction so we don't forget about that.