message: docs(usereactive): add the demo for showing computed properties of useReactive
  The get syntax binds an object property to a function that will be called when that property is
  looked up.
diff: @@ -22,9 +22,13 @@ It offers data reactivity when manipulating states and views, in which case `use
  <code src="./demo/demo2.tsx" />
  +### Computed Properties
  +
  +<code src="./demo/demo3.tsx" />
  +
  ### notice
  -<code src="./demo/demo3.tsx" desc="`useReactive` returns a proxy object which always has the same reference. If `useEffect`, `useMemo`, `useCallback` and props passed to child component rely on the proxy, none of the above will be invoked by any changes to the proxy." />
  +<code src="./demo/demo4.tsx" desc="`useReactive` returns a proxy object which always has the same reference. If `useEffect`, `useMemo`, `useCallback` and props passed to child component rely on the proxy, none of the above will be invoked by any changes to the proxy." />
  ## API
  