doc: fix Type notation in webstreams

Replace `type` with `Type: {Promise}`. Plus, fix incorrect
verb(`creates` -> `returns`) in description.

PR-URL: nodejs#49121
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Chemi Atlow <chemi@atlow.co.il>

doc/api/webstreams.md

@@ -895,7 +895,7 @@ added: v16.5.0
 
 * Returns: {WritableStreamDefaultWriter}
 
-Creates and creates a new writer instance that can be used to write
+Creates and returns a new writer instance that can be used to write
 data into the `WritableStream`.
 
 #### `writableStream.locked`
@@ -995,8 +995,8 @@ The amount of data required to fill the {WritableStream}'s queue.
 added: v16.5.0
 -->
 
-* type: A promise that is fulfilled with `undefined` when the
-  writer is ready to be used.
+* Type: {Promise} Fulfilled with `undefined` when the writer is ready
+  to be used.
 
 #### `writableStreamDefaultWriter.releaseLock()`