Write out the test in the README

[drj11]

Per my review on https://github.com/openjournals/joss-reviews/issues/2400

I agree with your comment on https://github.com/openjournals/joss-reviews/issues/2400#issuecomment-657416699 : gpp's documentation is a sufficient test of gpp. But It would be best for my conscience in checking the check box if this were more explicit.

I recommend:

• Put "GPP's own documentation uses GPP and generates HTML, LaTeX, and man pages (troff) from one gpp source file" in the first paragraph at the top of the README. It's a good feature of gpp and a useful demonstration of its capabilities.
• After the README's Documentation section add a Testing section: "gpp -H -Dhtml doc/gpp.pp -o gpp.html builds GPP's HTML document and serves as a basic test; for more see the doc/gpp.pp file".

[logological]

Thanks for the suggestion. I'd prefer not to mention this in the lede paragraph as I don't consider it central to the description of what GPP is. However, I've expanded the part of the README where I mention generating the documentation as a test of GPP's capabilities; as you suggested I explicitly gave the command to run and explicitly referenced the doc/gpp.pp file (with a hyperlink). Note that I didn't specifically instruct the user to generate the HTML version of the documentation, since running gpp -H gpp.pp without any further arguments will output a help message with the exact command lines to use to generate the troff, HTML, and LaTeX documentation:

 To get the man page, run:              
    gpp -H -Dman gpp.pp -o gpp.1    

 To get the HTML page, run:             
    gpp -H -Dhtml gpp.pp -o gpp.html

 To get a LaTeX version, run:           
    gpp -H -Dlatex gpp.pp -o gpp.tex

I've also opened a new issue (Issue #45) for a proper test suite, though as I mentioned in the review issue, I think this can be left as future work. (Hopefully I can get around to this some time in the next few weeks or months.)

I hope this is sufficient for you—if not, feel free to reopen this issue.