chore(docs): tweak intro paragraph copy (#10808)

docs/pages/getting-started/index.mdx

@@ -7,7 +7,9 @@ import manifest from "@/data/manifest.json"
 
 # What is Auth.js?
 
-Auth.js is a runtime agnostic library based on standard Web APIs that deeply integrates with modern JavaScript frameworks via additional libraries that wrap the core functionality and tailor it to the framework's best practices. This documentation covers `next-auth@5.0.0-beta` and later and all other frameworks under the `@auth/*` namespace. Documentation for `next-auth@4.x.y` can still be found at [next-auth.js.org](https://next-auth.js.org).
+Auth.js is a <abbr title="Designed to work seamlessly across different JavaScript runtime environments without relying on specific features or behaviors of any particular runtime">runtime agnostic</abbr> library based on standard Web APIs that integrates deeply with multiple modern JavaScript frameworks to provide an authentication experience that's simple to get started with, easy to extend, and always private and secure!
+
+This documentation covers `next-auth@5.0.0-beta` and later and all other frameworks under the `@auth/*` namespace. Documentation for `next-auth@4.x.y` can still be found at [next-auth.js.org](https://next-auth.js.org).
 
 Select your framework of choice to get started, or view the example application deployment or repository with the buttons below.