added a bit more documentation for a couple udfs

src/main/java/com/infochimps/hadoop/pig/geo/AttachGUID.java

@@ -25,7 +25,7 @@
 /**
    
    Given a qualifier (namespace + '.' + protocol + '.' + layer), a domain id field name (eg. 'geoname_id')
-   and a geoJSON entity, generates a guid for it. To do this the method parses the geoJSON, pulls out
+   and a geoJSON entity, generates an md5id for it. To do this the method parses the geoJSON, pulls out
    the value of the named id field from the properties HashMap and concatenates the qualifier and the
    domain id. If there is no domain id use a '-1'.
    
@@ -47,7 +47,7 @@ public String exec(Tuple input) throws IOException {
             return null;
 
         String qualifier = input.get(0).toString();
-        String id_field = input.get(1).toString(); // if this is -1, then the records are assumed to have no domain id. The full json of the object itself is used.
+        String id_field = input.get(1).toString(); // if this is -1 the json shouldn't contain it as a key
         String json = input.get(2).toString();
         String resultId = null;
         String result = null;
@@ -59,7 +59,7 @@ public String exec(Tuple input) throws IOException {
                 String domainId = feature.getProperties().getString(id_field);
                 resultId = constructGUID(qualifier, domainId);
             } else {
-                resultId = constructGUID(qualifier, json);
+                resultId = constructGUID(qualifier, json); // use the full json string itself
             }
             resultFeature = new GeoFeature(resultId, feature.getMfGeometry(), feature.getProperties());
             result = resultFeature.serialize();