Docs for arithmetic between magnitude systems

[PASEA-PG]

Description

This pull request is to add documentation to show how magnitude systems can be compared. This PR is work in progress.

Fixes #13248

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[pllim]

Hello! Since you said it is a work in progress, I have turned this PR to draft for now. Please take it out of draft when you are ready for review. Thanks!

[github-actions]

Welcome to Astropy 👋 and congratulations on your first pull request! 🎉

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[github-actions]

Hi humans 👋 - this pull request hasn't had any new commits for approximately 4 months. I plan to close this in 30 days if the pull request doesn't have any new commits by then.

In lieu of a stalled pull request, please consider closing this and open an issue instead if a reminder is needed to revisit in the future. Maintainers may also choose to add keep-open label to keep this PR open but it is discouraged unless absolutely necessary.

If this PR still needs to be reviewed, as an author, you can rebase it to reset the clock.

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[github-actions]

I'm going to close this pull request as per my previous message. If you think what is being added/fixed here is still important, please remember to open an issue to keep track of it. Thanks!

If this is the first time I am commenting on this issue, or if you believe I closed this issue incorrectly, please report this here.

[pllim]

I thought more docs would come but they never did. I pinged @aaryapatil for clarification.

[aaryapatil]

Thanks for the ping @pllim. Sorry for the delay on my end. I have this on my calendar to get done this week or next.

[pllim]

@aaryapatil , any progress? Thanks!

[pllim]

@aaryapatil , any update on this? Thanks!

[aaryapatil]

Sorry @pllim. Turns out the students don't have access to the PASEA-PG account (so the delay is on me, not the students!), and with my move across continents I have lost it as well. But I will really (really) get to this by the end of this year (once I am on track with the finance work I have pending...)