Add instructions for reviewers on how to update their information

[matthewfeickert]

:wave: Hi. As a current reviewer I don't know how to update my information in the reviewer spreadsheet

https://github.com/openjournals/joss/blob/1c8ea758fd5da98d780f6283ee6446c3ae892af5/docs/editing.md#L55

Is there a process to this? Can the preferred way (even if it is just emailing a member of the editorial board) be added to the reviewer docs?

[kthyng]

Hi @matthewfeickert! Currently please just email @arfon to update yourself in the reviewer spreadsheet. I'll leave this open regarding the suggestion to add this to the reviewer docs — good idea but I can't do it at the moment. Thanks!