Update Stylesheets make doc documentation

[ebeshero]

The Stylesheets README includes guidance on building Documentation for this repo by directoring the visitor to enter make doc, and outputting the built document at release/xslcommon/doc/tei-xsl/index.html. The built materials in xslcommon include guidance on how work with Stylesheets on conversions and a "Stylebear" tool (a web form that would let you input parameters to change, and generates a customized XSLT stylesheet), but that mechanism no longer works. (I don't know if I've ever seen the "Stylebear" in action.)

I'm opening this ticket to suggest we update / remove / fix this and other outdated documentation of the Stylesheets. We could remove the documentation entirely, but much of the information is helpful so long as we're still maintaining conversion scripts. But it's full of holes, too: Section 5's "Documentation of common conversions and start points" is a list of broken links.

Should we be guiding visitors to run make doc? If so, what documentation should we be providing in that build now?

Should we add a warning / caution in our README that some of the contents generated by make doc are obsolete?