Added note about or facets / default filters.

config/vufind/searches.ini

@@ -71,6 +71,10 @@ retain_filters_by_default = true
 ; The filters listed below will be applied to all new searches by default. Omit
 ; this setting to have no default filters applied. These differ from hidden
 ; filters because they are visible in the UI and may be removed by the user.
+;
+; NOTE: If you are setting a default filter on a field that is used for OR
+; facets (see the orFacets setting in facets.ini), be sure to prefix the field
+; name with a tilde (~)... e.g. "~format:Book"
 ;default_filters[] = "format:Book"
 ;default_filters[] = "institution:MyInstitution"