docs: set max width for man page paragraphs to 65ch

The man pages aren't displayed using the css for the rest of the site.
The man pages lines are too long to read comfortably. Limit line length.

Author: rouilj

doc/Makefile

@@ -19,6 +19,8 @@ man_html: $(MAN_HTML)
 
 html_extra/man_pages/%.1.html: ../share/man/man1/%.1
 	man --html=cat $< > $@
+	# set max width for paragraphs
+	sed -i '/<style/,/<\/style/s/\(p\s* { \)margin/\1max-width: 65ch; margin/' $@
 	#man2html $< > $@
 
 clean: