update guide in an instance where publisher file now is usable

[kcri...@gmail.com]

In https://github.com/PreTeXtBook/pretext/commit/2fa39bd6594069f85e158286347a61882334cc11 Rob gave some documentation on how to deal with an unusual situation one might have with LaTeX images.  However, it refers to command line parameters (and mentions they're going away), and in the meantime indeed that particular option is in the publisher file (documented in https://pretextbook.org/doc/guide/html/publication-file-latex.html#latex-page-options and https://pretextbook.org/doc/guide/html/page-shape.html).  

Would it be appropriate to open a PR to update that language (currently in https://pretextbook.org/doc/guide/html/debugging-pretext-image-generation.html)?