Small text fixes for enum.rst

[elliotwaite]

Some suggestions I thought of while reading over this helpful HOWTO.

If any of these changes are incorrect or unwanted, feel free to edit this PR or cherry-pick only the changes you want to keep.

[ethanfurman]

I made a couple changes to your changes, but overall it looks good! Thank you!

[elliotwaite]

Thanks for the review. Your changes look good.

That "whitespace or comma separated string" sentence is a tricky one because the value can be a whitespace-separated, comma-separated, or comma-and-whitespace-separated string. Listing all those options might be the clearest, but might be overly verbose given that the code example shown right after that sentence clears up the ambiguity. I see now how what I suggested actually made it worse since it suggested that the value could be a whitespace string or a comma-separated string. From looking at some Google search results, it looks like how you have it now or how you had it before are two popular ways to write that sentence if just deciding on hyphen placement.

[ambv]

At least as a non-native speaker, I prefer "whitespace- and comma-separated" because it clearly builds the sentence structure, making it easier to parse. Listing the whitespace+commas option feels a little verbose to me in this context. I think the current state is clear and reads well.

[bedevere-bot]

@ambv: Please replace # with GH- in the commit message next time. Thanks!

[elliotwaite]

@ambv, got it, sounds good. Thanks for the merge.