docs: revert hardcoded getting-started link to README.md

The link in the org-mode deprecation notice was hardcoded to
`../getting-started/` as a workaround for VitePress not resolving
README.md links. Now that #2765 adds a markdown-it rewrite rule
to handle this automatically, revert to the canonical `README.md`
reference.

Assisted-by: Claude
Signed-off-by: Wayne Sun <gsun@redhat.com>

Author: waynesun09

docs/guides/getting-started/org-mode.md

@@ -4,7 +4,7 @@ sidebar_position: 4
 
 # Per-Org Mode
 
-> **Planned deprecation.** Per-org installation mode will be deprecated in favor of per-repo installation ([ADR 0044](../../ADRs/0044-deprecate-per-org-installation-mode.md)). New installations should use the [per-repo Getting Started guides](../getting-started/). Existing per-org installations continue to work and are fully supported during the transition.
+> **Planned deprecation.** Per-org installation mode will be deprecated in favor of per-repo installation ([ADR 0044](../../ADRs/0044-deprecate-per-org-installation-mode.md)). New installations should use the [per-repo Getting Started guides](README.md). Existing per-org installations continue to work and are fully supported during the transition.
 
 The goal of this document is that you install Fullsend for your whole
 GitHub organization, so different repositories share inference and infrastructure.