chore(multi-key-map/README): sync with USAGE

@vates/multi-key-map/README.md

@@ -21,15 +21,20 @@ import { MultiKeyMap } from '@vates/multi-key-map'
 
 const map = new MultiKeyMap()
 
+const OBJ = {}
 map.set([], 0)
 map.set(['foo'], 1)
 map.set(['foo', 'bar'], 2)
 map.set(['bar', 'foo'], 3)
+map.set([OBJ], 4)
+map.set([{}], 5)
 
 map.get([]) // 0
 map.get(['foo']) // 1
 map.get(['foo', 'bar']) // 2
 map.get(['bar', 'foo']) // 3
+map.get([OBJ]) // 4
+map.get([{}]) // undefined
 ```
 
 ## Contributions