docs: fix wording in browser support description

Fixes #21144

Changed 'browsers that were released at least 2.5 years ago'
to 'features which have been available across browsers for at least 2.5 years'
to correctly describe what Baseline Widely Available means.

The previous wording suggested older browsers (>= 2.5 years old)
when it should describe features available for >= 2.5 years.

Author: hlongc

docs/guide/index.md

@@ -22,7 +22,7 @@ You can learn more about the rationale behind the project in the [Why Vite](./wh
 
 During development, Vite assumes that a modern browser is used. This means the browser supports most of the latest JavaScript and CSS features. For that reason, Vite sets [`esnext` as the transform target](https://esbuild.github.io/api/#target). This prevents syntax lowering, letting Vite serve modules as close as possible to the original source code. Vite injects some runtime code to make the development server work. These code use features included in [Baseline](https://web-platform-dx.github.io/web-features/) Newly Available at the time of each major release (2025-05-01 for this major).
 
-For production builds, Vite by default targets [Baseline](https://web-platform-dx.github.io/web-features/) Widely Available browsers. These are browsers that were released at least 2.5 years ago. The target can be lowered via configuration. Additionally, legacy browsers can be supported via the official [@vitejs/plugin-legacy](https://github.com/vitejs/vite/tree/main/packages/plugin-legacy). See the [Building for Production](./build) section for more details.
+For production builds, Vite by default targets [Baseline](https://web-platform-dx.github.io/web-features/) Widely Available browsers. That means it only uses features which have been available across browsers for at least 2.5 years. The target can be lowered via configuration. Additionally, legacy browsers can be supported via the official [@vitejs/plugin-legacy](https://github.com/vitejs/vite/tree/main/packages/plugin-legacy). See the [Building for Production](./build) section for more details.
 
 ## Trying Vite Online