[Feature]: Add missing trust-building pages to podman.io (positioning, adopters, security)

### Consisely describe the feature.

## Summary
While exploring podman.io, I noticed a few important pages that similar
open-source infra projects (Kubernetes.io, Docker's site, etc.) include,
which podman.io currently lacks. These would help new visitors know
and trust Podman faster.

## Suggestions

### 1. Adopters / Who's Using Podman
A page showcasing organizations running Podman in production — similar
to Kubernetes' Adopters page. Currently the Community page lists
*contributing* orgs (Red Hat, IBM, SUSE, etc.), but there's no visible
proof of production usage. This is often a key trust signal for teams
evaluating adoption.

### 2. "Why Podman" / Positioning Page
A dedicated page explaining Podman's core differentiators (daemonless
architecture, rootless containers, OCI compliance, Kubernetes-native
pod support) in one place. Right now this info is scattered across the
homepage, Features page, and docs. A single clear positioning page
would help visitors quickly understand what makes Podman's approach
different, and could surface the existing "Usage Transfer" doc
(command mapping) which is currently buried and hard to find.

### 3. Security Policy / CVE Disclosure Page
No dedicated page explaining the security model or how to report
vulnerabilities, despite "Secure" being one of the four homepage
highlights. A clear security policy page (disclosure process, CVE
advisories, rootless security model explanation) would reinforce
that claim with substance.

## Why this matters
These are common trust/credibility touchpoints on similar project
sites, and their absence may cause evaluators to look elsewhere for
this information — or worse, assume it doesn't exist.

Happy to help draft content/copy for any of these if useful!

### Upload screenshots

Add screenshots or proposed mockups (optional).

### LLM Policy

- [x] This issue is human-written, and folow up comments will also be human-written

Start by reviewing the podman.io homepage, Community page, Features page, and the existing Usage Transfer documentation to understand the current information architecture. Define the scope and content for adopters, positioning, and security pages, then verify that each is published, discoverable, and covers the trust information described in the issue.

Written by the indexing model from the issue text.