update doc

Author: skywind3000

README.md

@@ -60,7 +60,9 @@ You will see the result in the command line.
 | g:gpt_commit_model | - | `'gpt-3.5-turbo'` | ChatGPT model |
 | g:gpt_commit_staged | - | `1` | set to 1 to use staged diff |
 | g:gpt_commit_max_line | - | `160` | max diff lines to reference |
-| g:gpt_commit_url | - | `''` | openai request url |
+| g:gpt_commit_url | - | `''` | alternative request URL, see #1 |
+
+Note #1: the default URL is "https://api.openai.com/v1/chat/completions", can be changed by setting `g:gpt_commit_url`.
 
 ## Script
 
@@ -85,12 +87,12 @@ available options:
 
 If you find this plugin amusing, you might also be interested in my other vim plugins, such as:
 
-- [asynctasks.vim](https://github.com/skywind3000/asynctasks.vim): Modern Task System for Project Building/Testing/Deploying.
 - [vim-auto-popmenu](https://github.com/skywind3000/vim-auto-popmenu): Display the Completion Menu Automantically.
 - [vim-color-export](https://github.com/skywind3000/vim-color-export): A tool to backport NeoVim colorschemes to Vim. 
 - [vim-color-patch](https://github.com/skywind3000/vim-color-patch): Load colorscheme patch script automatically.
 - [vim-navigator](https://github.com/skywind3000/vim-navigator): Navigate Your Commands Easily.
 - [vim-rt-format](https://github.com/skywind3000/vim-rt-format): Prettify Current Line on Enter.
 - [vim-quickui](https://github.com/skywind3000/vim-quickui): The missing UI extensions for Vim 8.2 (and NeoVim 0.4).
+- [asynctasks.vim](https://github.com/skywind3000/asynctasks.vim): Modern Task System for Project Building/Testing/Deploying.