debian/rules.real: Update install-doc rule for change to Sphinx HTML output

I can't see when or why this changed, but the HTML (and related) files
are now being generated in Documentation/output and not an html
subdirectory of that.

debian/rules.real

@@ -240,8 +240,9 @@ install-doc: $(STAMPS_DIR)/build-doc
 	find * -name '*.html' -print | \
 	cpio -pd --preserve-modification-time '$(CURDIR)/$(OUT_DIR)/html/oldstyle'
 	set -o pipefail; \
-	cd $(DIR)/Documentation/output/html; \
-	find * -name objects.inv -prune -o -print | \
+	cd $(DIR)/Documentation/output; \
+	find * -name '*.rst' -prune -o -name objects.inv -prune \
+		-o -name xml -prune -o -print | \
 	cpio -pd --preserve-modification-time '$(CURDIR)/$(OUT_DIR)/html/newstyle'
 	gzip -9nqfr $(OUT_DIR)/Documentation
 	+$(MAKE_SELF) install-base