Changes to the FITS-header Tutorial

[saimafsiddiqui]

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[mwcraig]

Hi 👋 @saimafsiddiqui and thanks for this pull request! It is good to have people taking a fresh look at these tutorials.

I have several suggestion below -- mostly very minor. FITS is a weird file format, in that it is strict in some ways (keywords can have no more than 8 characters) but very loose in others (images can be in any HDU), so I tried to note some cases where you will want to be a little less broad in how you talk about fits.

Thanks again for working on this!

[mwcraig]

I'm not sure I agree that this is the easiest -- if you just need the header or data alone and don't need to modify the file, then maybe it is more convenient. If you want to change the file, though, I think fits.open is probably preferable.

[saimafsiddiqui]

Thank you! I'll change how I wrote that and add a little more about the functions for clarity.

[eblur]

@mwcraig Can you check that your changes were implemented properly? If not, I'll contact Saima so we can upload her updates.