bin/: add kind, gated on rootless Docker availability

kind needs a container runtime to create clusters, so only install it
when a rootless Docker daemon is actually reachable (SecurityOptions
reports name=rootless). Otherwise skip with a note.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -31,7 +31,8 @@ Already have a clone? Just run it directly:
   `credential.helper store` (plaintext `~/.git-credentials`, 0600) for
   HTTPS auth.
 - `bin/` — installs userland devops CLIs (jq, kubectl, helm, k9s,
-  kubectx/kubens, stern, yq, OpenTofu, terragrunt) as self-contained,
+  kubectx/kubens, stern, yq, OpenTofu, terragrunt, plus kind when rootless
+  Docker is available) as self-contained,
   statically linked release binaries into `~/.local/bin`. No sudo, nothing
   outside `$HOME`, so they persist across Kasm redeploys with no reinstall.
   Idempotent: each tool records its version under `~/.local/bin/.versions`