Add term to public_bookcase (#1333)

Co-authored-by: Coehill <thomas@thomascraig.dev>

Author: Coehill

data/presets/amenity/public_bookcase.json

@@ -36,7 +36,8 @@
         "bookcrossing",
         "library",
         "share a book",
-        "sharing books"
+        "sharing books",
+        "little free library"
     ],
     "tags": {
         "amenity": "public_bookcase"