Move man/ChangeLog to man/po/ChangeLog

Shuffle contents between man/ChangeLog and the main ChangeLog,
where they belong. Fix pointers to the po/ChangeLog dirs in
README.translators.

README.translators

@@ -2,7 +2,7 @@ Translators, when adding/updating your translation files, please follow
 the following rules:
 
 * Update debian/changelog and one of po/ChangeLog, dselect/po/ChangeLog,
-  scripts/ChangeLog or man/ChangeLog:
+  scripts/po/ChangeLog or man/po/ChangeLog:
 
   - Beware the you should NOT update the main ChangeLog file
     for translation updates. Use the ChangeLog in the relevant