Update README with note on repository fork

Add a prominent note about this repo being a fork with improvements.

README.md

@@ -11,6 +11,14 @@
 
 <!-- panvimdoc-ignore-end -->
 
+---
+
+> **Note:** This repository is a fork of the original [gp.nvim](https://github.com/Robitx/gp.nvim) plugin. It includes a few small improvements which you can find in the [GitHub compare page](https://github.com/Robitx/gp.nvim/compare/main...argshook:gp.nvim:main).
+
+> If you like this plugin, please share your love on the original repository: [gp.nvim](https://github.com/Robitx/gp.nvim)
+
+---
+
 <br>
 
 **ChatGPT like sessions, Instructable text/code operations, Speech to text and Image generation in your favorite editor.**
@@ -105,19 +113,20 @@ require("gp").setup()
 
 -- shortcuts might be setup here (see Usage > Shortcuts in Readme)
 ```
+
 ## 2. OpenAI API key
 
 Make sure you have OpenAI API key. [Get one here](https://platform.openai.com/account/api-keys) and use it in the [4. Configuration](#4-configuration). Also consider setting up [usage limits](https://platform.openai.com/account/billing/limits) so you won't get suprised at the end of the month.
 
 The OpenAI API key can be passed to the plugin in multiple ways:
 
-| Method                    | Example                                                        | Security Level      |
-| ------------------------- | -------------------------------------------------------------- | ------------------- |
-| hardcoded string          | `openai_api_key: "sk-...",`                                    | Low                 |
-| default env var           | set `OPENAI_API_KEY` environment variable in shell config      | Medium              |
-| custom env var            | `openai_api_key = os.getenv("CUSTOM_ENV_NAME"),`               | Medium              |
-| read from file            | `openai_api_key = { "cat", "path_to_api_key" },`               | Medium-High         |
-| password manager          | `openai_api_key = { "bw", "get", "password", "OAI_API_KEY" },` | High                |
+| Method           | Example                                                        | Security Level |
+| ---------------- | -------------------------------------------------------------- | -------------- |
+| hardcoded string | `openai_api_key: "sk-...",`                                    | Low            |
+| default env var  | set `OPENAI_API_KEY` environment variable in shell config      | Medium         |
+| custom env var   | `openai_api_key = os.getenv("CUSTOM_ENV_NAME"),`               | Medium         |
+| read from file   | `openai_api_key = { "cat", "path_to_api_key" },`               | Medium-High    |
+| password manager | `openai_api_key = { "bw", "get", "password", "OAI_API_KEY" },` | High           |
 
 If `openai_api_key` is a table, Gp runs it asynchronously to avoid blocking Neovim (password managers can take a second or two).