Fix typo

Fixes typo "artowrk" and changed the sentence to be more similar to other layers.

See also https://taginfo.openstreetmap.org/search?q=artowrk#values

assets/layers/artwork/artwork.json

@@ -154,7 +154,7 @@
       "freeform": {
         "key": "artwork_type",
         "addExtraTags": [
-          "fixme=Artowrk type was added with the freeform, might need another check"
+          "fixme=Freeform field used for artwork type - doublecheck the value"
         ]
       },
       "mappings": [
@@ -558,4 +558,4 @@
       }
     }
   ]
-}
+}