Revision to Sticker back specification

[Magnus Forsberg]

Found here:
https://www.ldraw.org/docs-main/ldraw-or...ndard.html

- Reformatted for clarity.
- Explicitly stated orientation 
- Added optional suffix to naming convention for non-square/rectangular boxes.

Could you please add a link to this page, from https://www.ldraw.org/article/512.html#sticker_geo