docs: archive notice pointing at the release pipeline

[bchalios]

Prepends an archive notice to the README ahead of archiving this repository: releases are built by the fc-versions pipeline in e2b-dev/infra under the vX.Y-<major.minor.patch> scheme and published to the public artifact bucket; the branches and tags here stay readable for reference.

Deliberately does not say where fork development moved — no private-repo references in public text.

Merge, then: archive the repository and remove it from the App installation (org-admin actions).

[cursor]

PR Summary

Low Risk
Documentation-only README change with no runtime, security, or data-handling impact.

Overview
The README now opens with a GitHub IMPORTANT callout stating the repository is archived. It directs readers to E2B Firecracker builds from the fc-versions pipeline in e2b-dev/infra, the vX.Y-<major.minor.patch> release naming, and publication to gs://e2b-artifact-binaries/firecrackers/, and notes that branches and tags here stay for reference while legacy vX.Y.Z_<sha> builds from this repo get no further updates. A horizontal rule separates that notice from the existing logo and project content.

^{Reviewed by Cursor Bugbot for commit 7a2ae43. Bugbot is set up for automated code reviews on this repo. Configure here.}

[claude]

Additional findings (outside the current diff — GitHub can't attach inline comments there):

• 🟡 README.md — New archive notice (lines 1-7) contradicts the untouched '## Releases' section: it says releases here get 'no further updates' and real releases now come from e2b-dev/infra's fc-versions pipeline, but lines 89-94 still tell readers 'New Firecracker versions are released via the GitHub repository releases page ... typically every two or three months' and point at docs/RELEASE_POLICY.md as if this repo's release process is still active.

  Extended reasoning...

  A reader who scrolls past the top banner reaches the Releases section and is told, contrary to the banner, that this repo actively cuts new releases every 2-3 months per docs/RELEASE_POLICY.md; they file issues/PRs expecting new releases here or rely on stale release-policy timing, whereas before this diff there was no such contradiction (the repo's own docs consistently described it as active). A correct fix updates or removes the Releases section text so it matches the new archived/frozen status stated in the banner.

  Verification: nit. The new archive banner at README.md:1-7 says "This repository is archived ... receive no further updates," while the untouched Releases section at README.md:89-94 still says "New Firecracker versions are released via the GitHub repository [releases] page, typically every two or three months" and points at docs/RELEASE_POLICY.md as an active policy. Within the merged README these two passa