docs(update): remove unsupported --check command

[helix4u]

Summary

• remove the stale \ example from the update guide
• keep the docs aligned with the current CLI, which only supports \
• continue pointing readers to \ and GitHub releases for version checks

Context

The current docs advertise , but the command is not implemented in this branch. That led directly to backlog confusion in support.

There is already an open upstream PR to add the flag for real: #7299. This docs PR is just a stopgap so the published guidance matches current behavior until that lands.

Testing

• not run (docs-only change)

[kshitijk4poor]

Merged via PR #11134. Your commit was cherry-picked onto current main with your authorship preserved in git log. Thanks @helix4u!