convert "supported hardware" to an appendix

doc/Makefile

@@ -12,8 +12,8 @@ DOCS=\
 
 hardware.adoc: hardware.nix
 	pandoc -f rst -t asciidoc -o $@ hardware.rst
-	# don't even ask
-	sed -E -i.bak -e 's/^=(=*) /\1 /g' hardware.adoc
+	# sections in an appendix need to start at ===
+	sed -E -i.bak -e 's/^(=*) /=\1 /g' hardware.adoc
 
 html: Makefile  $(patsubst %,%.adoc,$(DOCS))
 	asciidoctor  -D _build -d book index.adoc