Add notes about coding style and submission guidelines. As became clear from recent conversation, matching submitted code to the format of the existing code is not an obvious thing to do. (It should be but apparently it just doesn't occur to people.) Some description of the coding style is now present in the README. Additionally, submission guidelines have also been added to make it clear that patches (diffs) are the preferred means of providing code changes.

all:
	hg rm manual/* || true
	rm -f manual/*.pdf manual/*.html
	docbook2html -o manual manual.docbook.sgml
	docbook2html -u manual.docbook.sgml && mv manual.docbook.html manual/manual.html
	docbook2pdf -u manual.docbook.sgml && mv manual.docbook.pdf manual/manual.pdf
	rm -f manual.docbook.html
	hg add manual/*