improve docs generation, including PDF output

- Fix the manual build rules (missing the .xsl as an input).
- Add a README describing how the docs build works.
- Add rules that generate PDF, just 'cause we can.

1 files changed, 11 insertions, 0 deletions

diff --git a/doc/README.md b/doc/README.md
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+This directory contains the Ninja manual and support files used in
+building it.  Here's a brief overview of how it works.
+
+The source text, `manual.asciidoc`, is written in the AsciiDoc format.
+AsciiDoc can generate HTML but it doesn't look great; instead, we use
+AsciiDoc to generate the Docbook XML format and then provide our own
+Docbook XSL tweaks to produce HTML from that.
+
+In theory using AsciiDoc and DocBook allows us to produce nice PDF
+documentation etc.  In reality it's not clear anyone wants that, but the
+build rules are in place to generate it if you install dblatex.