docs: add global arg for wrangler --cmd

[pi0]

Summary

This PR adds new (upcoming) --cwd option for wrangler CLI.

Context: cloudflare/workers-sdk#7994

Screenshots (optional)

Documentation checklist

• The documentation style guide has been adhered to.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[CarmenPopoviciu]

@pi0 thank you so much for opening this PR ♥️ . Let's please hold off merging until cloudflare/workers-sdk#7994 is merged and released. I'll circle back here myself when that is done and get this over the finish line

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