Give each template its own README

The root README keeps what is shared — dependencies, accessibility, the
scripts — and links to a per-template README for how to build and what is
in it. The Posters section moves to poster_template/README.md with a
pointer left behind, since it is that template's caveat.

slides_template/README.md replaces the two READMEs that came with
beamer-mako.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

paper_template/README.md

@@ -0,0 +1,34 @@
+# Paper Template
+
+A paper in the standard `article` class, styled by `cdsc-paper.sty`. See the
+[root README](../README.md) for tagging and accessibility.
+
+```
+make            # build the PDF
+make vc         # write a vc file with the current git revision
+make clean
+```
+
+`text.tex` carries worked examples of alt text on a figure and a tagged table
+header row. Delete that section when you start writing.
+
+## Fonts
+
+Libertinus Serif and TeX Gyre Heros, both from `texlive-fonts-extra`.
+
+Mako prefers [Adobe Garamond Premier
+Pro](https://fonts.adobe.com/fonts/garamond-premier-pro), which is commercial
+and not redistributable. If you have it installed, swap the `\setmainfont` line
+in `text.tex`. CDSC members can ask Mako for the files.
+
+## Bibliography
+
+biblatex with biber, APA style, reading `refs.bib`. `\citepos` and `\citespos`
+give possessive citations.
+
+## Version footer
+
+`make vc` writes a `vc` file from the current git revision. Uncomment the
+`\input{vc}` and `\pagestyle{cdsc-page-git}` lines in `text.tex` to print it at
+the foot of each page. On Overleaf, use `\pagestyle{cdsc-page-overleaf}`
+instead, which stamps the build time.