docs: updates README.md

Adds a banner and an allowed regexp pattern for presets' names.

Author: rasulomaroff

README.md

@@ -1,6 +1,8 @@
 <h1 align="center">reactive.nvim</h1>
 <p align="center"><sup>Reactivity. Right in your neovim.</sup></p>
 
+![reactive](https://github.com/rasulomaroff/reactive.nvim/assets/80093436/42565d8a-68d1-4bee-832b-7c5e379dbe01)
+
 <div align="center">
   <img src="https://img.shields.io/badge/Made%20with%20Lua-blueviolet.svg?style=for-the-badge&logo=lua">
   <img src="https://img.shields.io/github/stars/rasulomaroff/reactive.nvim?style=for-the-badge">
@@ -192,7 +194,7 @@ The `name` field is required.
 
 | Property  | Type                                                                  | Description                                                                                                                                                                                                                                                                             |
 |-----------|-----------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
-| name      | `string`                                                              | This is your preset's name. It should be unique across other presets.                                                                                                                                                                                                                   |
+| name      | `string`                                                              | This is your preset's name. It should be unique across other presets. Regexp pattern: `[a-zA-Z0-9_-]`.                                                                                                                                                                                  |
 | lazy      | `boolean`                                                             | This property is meant to be used by other plugin developers. By making your preset lazy you can delay its usage till a user decides to activate it.                                                                                                                                    |
 | priority  | `number`                                                              | You can set a priority of any preset, if you faced conflicting preset highlights, for example. It's not recommended to set this field, if you are a plugin developer.                                                                                                                   |
 | skip      | `fun(): boolean` or `{ winhl?: fun(): boolean, hl?: fun(): boolean }` | This function will be called on every mode change, so that you can define when your preset shouldn't be applied. It should return true, if you want to skip applying highlights. You can also pass a table with functions, if you want to disable only window highlights or highlights. |