docs: update README.md

README.md

@@ -798,7 +798,7 @@ The raw plugin text editing method `Prompt` has following signature:
 ---@param prompt string | nil  # nil for non interactive commads
 ---@param whisper string | nil  # predefined input (e.g. obtained from Whisper)
 ---@param callback function | nil  # callback(response) after completing the prompt
-Prompt(params, target, agent, template, prompt, whisper)
+Prompt(params, target, agent, template, prompt, whisper, callback)
 ```
 
 - `params` is a [table passed to neovim user commands](https://neovim.io/doc/user/lua-guide.html#lua-guide-commands-create), `Prompt` currently uses:
@@ -911,4 +911,5 @@ Prompt(params, target, agent, template, prompt, whisper)
 - `whisper`
   - optional string serving as a default for input prompt (for example generated from speech by Whisper)
 - `callback`
-  - optional callback function receiving the prompt response
+  - optional callback function allowing post processing logic on the prompt response  
+    (for example letting the model to generate commit message and using the callback to make actual commit)