Add Supplemental Documentation for TypeScript

[chacha912]

Description:

While the yorkie documentation includes information on TypeScript, it would be helpful to provide an explanation on the usage of JSONElement types. Yorkie-js-sdk uses a proxy, and to use methods like array.insertAfter and array.insertBefore that are not available in the native JS type, specifying the type as JSONElement is necessary.

type DocType = {
  list: JSONArray<number>;
};

const doc = new yorkie.Document<DocType>('sample-doc');
doc.update((root) => {
  root.list = [0, 1]; 
  root.list.push(2);  
});
doc.update((root) => {
  // to use methods like `getElementByIndex` and `moveAfter`, the type should be specified as `JSONArray`
  const prev = root.list.getElementByIndex(0);
  const item = root.list.getElementByIndex(1);
  root.list.moveAfter(prev.getID(), item.getID());
});

[hackerwins]

I recently heard about a bug with Array.Move that doesn't seem to be converging. It would be good to fix the bug and then add it to the documentation.