Add encoding specifier to Russian man page

See GH-341

doc/manual-src/ru/Makefile.am

@@ -126,6 +126,7 @@ text:
 
 man:
 	$(SPHINXBUILD) -b man $(ALLSPHINXOPTS) $(BUILDDIR)/man
+	sed -i -e '1i .\\" -*- mode: troff; coding: utf-8 -*-' $(BUILDDIR)/man/aria2c.1
 	@echo
 	@echo "Build finished. The manual pages are in $(BUILDDIR)/man."