clarify normal POI vs. landmark

To avoid confusion, we should not list the same types of places in both
descriptions. Also, borrowed some text from the REST API description of
what landmarks are exactly.

Author: incanus

MapboxGeocoder/MBPlacemarkScope.h

@@ -22,9 +22,9 @@ typedef NS_OPTIONS(NSUInteger, MBPlacemarkScope) {
     MBPlacemarkScopeNeighborhood = (1 << 7),
     /// A physical address, such as to a business or residence.
     MBPlacemarkScopeAddress = (1 << 8),
-    /// A point of interest, such as a business, school, or place of worship.
+    /// A point of interest, such as a business or school.
     MBPlacemarkScopePointOfInterest = (1 << 9),
-    /// A point of interest, such as school or place of worship -- subset of MBPlacemarkScopePointOfInterest
+    /// Subset of regular points of interest. Landmarks are particularly notable or long-lived features like parks, museums and places of worship.
     MBPlacemarkScopePointOfInterestLandmark = (1 << 10),
 
     /// All scopes.