Adds code to underscores generating subscript text when exporting as a
PDF file. The template now states the date README.org was published as
a PDF file.
Theses changes are not seen when the repository is viewed in the
browser. These changes are when/if the file is exported (mostly as a
PDF file but not exclusive to it). The publish date is for quickly
checking which version of the README file is the newer one if I have
several copies of it -- for some reason. The subscript change is an
appearance change. The file is more likely going to need underscores
displayed as underscores than used as a way to denote some subscript
text. Either way, this is an easy change in the future if things
change.