Rename README with proper file extension.

The README is written in asciidoc. At the times, IIRC GitHub didn't support
that markup format, but nowadays it's a good idea to name the file properly.

Author: dimitri

Makefile

@@ -14,7 +14,7 @@ ARCHIVE= $(DEBDIR)/export/$(PKGNAME)-$(VERSION).tar.gz
 
 doc: README.html
 
-README.html: README
+README.html: README.asciidoc
 	asciidoc -a toc -o $@ $<
 
 install: doc