Bug 861582: Missing description in the "Bug Fields" page for "Importance"

template/en/default/bug/field-help.none.tmpl

@@ -76,6 +76,10 @@ estimated_time =>
   "The amount of time that has been estimated it will take to resolve
    this ${terms.bug}.",
 
+importance =>
+  "The importance of $terms.abug is described as the combination of
+   its $vars.field_descs.priority and ${vars.field_descs.bug_severity}.",
+
 keywords =>
    "You can add keywords from a defined list to $terms.bugs, in order"
    _ " to easily identify and group them.",

template/en/default/pages/fields.html.tmpl

@@ -181,6 +181,11 @@
                                     field => field } %]
 [% END %]
 
+[%# This field is not a real one, but its label is visible in bugs. %]
+
+[% field_help_map.Importance = { help  => help_html.importance,
+                                 field => "importance" } %]
+
 [%# These are fields that don't need to be documented, either because
   # they have docs somewhere else in the UI, or they don't show up on bugs. 
   # %]