Clarify formatting requirement for BOSC abstracts

[nlharris]

In https://github.com/OBF/bosc_materials/blob/master/BOSC_review_process.md, the "Acceptance criteria" include

Correctly formatted: Abstracts must be in PDF format, are limited to two 8.5x11” or A4 pages (for BOSC 2021) and should include the title, author name(s), open source license, and code or project URL. Accepted abstracts are published on the BOSC website as-is.

In fact, although we can (and have) summarily reject abstracts that blatantly violate the format requirements (e.g. a 7-page paper), we don't reject abstracts that lack metadata such as author names, URL, etc.; we just request that they add that info. This criterion should probably be moved from "Acceptance criteria" to "Additional criteria" next year.

[nlharris]

#31 fixes this in the review process md

Also need to remember to change in the review form in EasyChair next year.