promote forum request to todo item so it is not lost

doc/todo/command_line_interface_for_required_content_setthings.mdwn

@@ -0,0 +1,11 @@
+Someone in the forum noticed that `git annex wanted`
+handles preferred content settings, but there is no analagous `git annex
+required`.
+
+Probably worth adding that, although required content is not an often 
+used feature, and vicfg can already configure it.
+
+(I don't much like the `git annex required` name. Nor the `git annex wanted`
+one when it comes to that. Oh well.)
+
+--[[Joey]]