chore: document function types

README.md

@@ -53,8 +53,7 @@ AIChat will automatically load `functions.json` and execute functions located in
 
 Now you can interact with your LLM using natural language prompts that trigger your defined functions.
 
-![demo](https://github.com/sigoden/aichat/assets/4012553/9a5df031-530a-4679-acdd-c8f0c45d2bf7)
-
+![image](https://github.com/sigoden/llm-functions/assets/4012553/867b7b2a-25fb-4c74-9b66-3701eaabbd1f)
 
 ## Writing Your Own Functions
 
@@ -86,6 +85,24 @@ The relationship between flags/options and parameters in function declarations i
 
 **After creating your function, don't forget to rebuild the function declarations.**
 
+## Function Types
+
+### Retrieve Type
+
+The function returns JSON data to LLM for further processing.
+
+AIChat does not ask permission to run the function or print the output.
+
+### Execute Type
+
+The function does not return data to LLM. Instead, they enable more complex actions, such as showing a progress bar or running a TUI application.
+
+AIChat will ask permission before running the function.
+
+![image](https://github.com/sigoden/aichat/assets/4012553/711067b8-dd23-443d-840a-5556697ab075)
+
+**AIChat categorizes functions starting with `may_` as `execute type` and all others as `retrieve type`.**
+
 ## License
 
 The project is under the MIT License, Refer to the [LICENSE](https://github.com/sigoden/llm-functions/blob/main/LICENSE) file for detailed information.