Elaborate on group purpose, add GH discussions link

This change adds introductional text to elaborate on the group's
raison d'être based on initial feedback we received on social media
immediately after launch.

The change also adds a reference to our newly started GH discussions
boards for engaging with the group on generic topics not related to
existing specs and docs.

Signed-off-by: Thilo Fromm <thilofromm@microsoft.com>

Author: t-lo

content/_index.md

@@ -7,10 +7,25 @@ BookToC: false
 
 # The Linux Userspace API (UAPI) Group
 
-The userspace API ("uapi") group is a community for people with an interest in innovating how we build, deploy, and run modern Linux operating systems.
+The userspace API ("uapi") group is a cross-distro community for people with an interest in innovating how we build, deploy, run, and safely update modern Linux operating systems.
 It serves as a central gathering place for specs, documentation, and ideas.
 
-Follow [@uapi-group](https://twitter.com/uapi-group) on twitter to catch the latest news!
+In scope of the group are secure boot mechanisms, kernel / disk image formats, TPM usage, safe and secure updates, and related topics.
+The group also cares about interop of image-based and/or immutable Linux distributions.
+
+The group was founded to discuss and align on common mechanisms, to prevent creating quasi standards by going with implementations first.
+Interested engineers are invited to join the discussions, and to represent the directions and interests of their projects and distributions.
+
+## Engage with the Group
+
+Our main means of engagement is Github.
+Please check out the group's [Github discussions](https://github.com/orgs/uapi-group/discussions) for general ongoing conversations - don't hesitate to tune in and share your thoughts!
+Feel free to start a new discussion if none exists for whatever brings you here - but please keep the group's focus in mind and do not stray off-topic.
+
+To engage with specific content please file issues and / or PRs directly to the [specifications](https://github.com/uapi-group/specifications/),
+[docs](https://github.com/uapi-group/docs/), and [kernel feature ideas](https://github.com/uapi-group/kernel-features/) repositories, respectively.
+
+To stay up to date on the group's activities there's also a Twitter account you can follow: [@uapi-group](https://twitter.com/uapi-group).
 
 ## UAPI Group Specifications