Explain `in_span` more for ruby docs

[cartermp]

It will set the status and record an exception for you, so this is worth mentioning and explaining in the status section as well.

[kennykguo]

if this issue is still active, please assign this issue to me, thanks

[svrnm]

Please note that we are not assigning issues, as per our contribution guidelines, if you are interested to work on this issue let us know, and we keep track and wait for a PR from you.