make_pdfs.sh makes a pdf of the README

[LukeRoantree4815162342]

change the shell script to exclude the readme

[ChrisspyB]

Rather than explicitly excluding the readme.md (and also contributing.md and any other .md's that sneak their way in) it might be better to generate files into a new folder, and have the bash script run on all .md files in there. This would also be helpful in keeping new worksheets together, and prevent remaking pdfs of existing .mds.

Edit: Though ideally we would just run make-pdf on each <my_new_worksheet.md> as soon as they are created.

[LukeRoantree4815162342]

That sounds like a much better plan, let's do that. Although I was holding off on integrating md2pdf directly, just in case we switch to something else. I was going to put a PR for python3 compatability, but saw there already has been one since January - unmerged. So we might need to look at switching to something else