📚 Add more themes

We'd love to expand our themes with new, cool ones! If you have a fancy theme in mind or would like to see and design new themes, here are simple instructions on how to get started. [(Here are the currently available themes.)](https://github.com/0l1v3rr/github-readme-tech-stack/blob/master/docs/THEMES.md)

### Requesting a theme
1. Open an issue describing your new theme. If possible, include an image. It can be a theme from another README card project.
2. Indicate in the issue if you want someone else to add the theme.

### Adding the theme
1. Fork the repository
2. Clone your fork
3. Locate the [`themes.ts`](https://github.com/0l1v3rr/github-readme-tech-stack/blob/master/src/const/themes.ts) file
4. Set your theme colors using the `themes.set()` function
5. Add your new theme to the [`THEMES.md`](https://github.com/0l1v3rr/github-readme-tech-stack/blob/master/docs/THEMES.md) file
6. Commit and push your changes
7. Open a [Pull Request](https://github.com/0l1v3rr/github-readme-tech-stack/pulls) containing your changes. Please also include a screenshot of your new theme in the PR.

**`themes.set()` example:**
```ts
// the theme name should be snake_case
themes.set("theme_name", {
backgroundColor: "#ffffff", // the background color of the card
borderColor: "#ffffff", // the border color of the card
titleColor: "#ffffff", // the title color
badgeColor: "#ffffff", // the background color of the badges
});
```

#### Additional context
- Please follow the structure of the code and make sure the spacing and formatting is consistent.
- The theme will not display correctly in THEMES.md until it is deployed, but you can test it locally. Your added theme will be available when your PR is merged.
- Be sure to check the previously added themes to see if a similar (or identical) theme already exists.
- This issue should remain open, please do not mark it as `fixed`.

The work is in src/const/themes.ts, where themes are defined with the themes.set() function. Check existing themes for structure, then add a new theme object with your chosen colors. Update docs/THEMES.md to list the new theme, and test locally. A screenshot of the new theme should be included in the pull request.

索引モデルが issue の本文から書いたものです。