Update readme.md w alias example (#24)

As fetching wrong alias format is returning 400, this example may save a few minutes and nerves of searching...

README.md

@@ -76,7 +76,7 @@ matrixClient.clientOpts = {
 const ydoc = new Y.Doc();
 const provider = new MatrixProvider(ydoc, matrixClient, {
  type: "alias",
- alias: "matrix-room-alias",
+ alias: "#matrix-room-alias:matrix.org",
 });
 provider.initialize();