docs(web-api): note the chat stream buffer size default (#2418)

Author: zimeg

packages/web-api/src/WebClient.ts

@@ -515,6 +515,8 @@ export class WebClient extends Methods {
    *
    * @description The "chatStream" method starts a new chat stream in a conversation that can be appended to. After appending an entire message, the stream can be stopped with concluding arguments such as "blocks" for gathering feedback.
    *
+   * The "markdown_text" content is appended to a buffer before being sent to the recipient, with a default buffer size of "256" characters. Setting the "buffer_size" value to a smaller number sends more frequent updates for the same amount of characters, but might reach rate limits more often.
+   *
    * @example
    * const streamer = client.chatStream({
    *   channel: "C0123456789",