doc: improve None condition doc for checked_div and checked_rem

[tspiteri]

This commit improves the condition mentioned in the docs for which checked_div and checked_rem return None.

For signed division, the commit changes "the operation results in overflow" to "the division results in overflow", otherwise there is room for misinterpretation for checked_rem: Without considering overflow, MIN % -1 would be simply zero, allowing the misinterpretation that "the operation" does not result in overflow in this case. This ambiguity is removed using "when the division results in overflow".

For unsigned division, the condition for None should be simply when rhs == 0, as no other overflow is possible.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @aidanhs (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[aidanhs]

r? @steveklabnik maybe?

[frewsxcv]

makes sense to me! thanks for clarifying this

@bors r+ rollup

[bors]

📌 Commit f2c5472 has been approved by frewsxcv