docs: add HTTP Request note for PostBin content visibility

[javienc]

Description

This PR enhances the Step five: Output data from your workflow section of the First Workflow tutorial by adding an informational note to help users actually see their custom body content on PostBin. Because the built‑in PostBin node only displays request headers, the new note shows how to use an HTTP Request node (Method POST, Send Body enabled, Body Content Type JSON) with the correct expression so that the message appears in the PostBin UI—all without removing any of the original tutorial steps.

Background

Addresses issue #11836: the PostBin node’s Send a request operation issues a GET request and omits the body, preventing users from seeing their message.

Multiple users have reported being unable to complete the Quick Start “longer introduction” tutorial because of this behavior.

Changes

• Inserted a note | PostBin content visibility block immediately after the numbered steps in Step five, explaining:
  • How to add an HTTP Request node on a branch.
  • Which parameters to set (Method POST, URL https://www.postb.in/<YOUR_BIN_ID>, enable Send Body, set Body Content Type to JSON, choose Using JSON under Specify Body).
  • The exact JSON snippet to paste into the editor:

    {
      "message": "There was a solar flare of class {{$json["classType"]}}"
    }

• Kept all existing PostBin instructions intact—this simply supplements them with a working alternative.

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[CLAassistant]

All committers have signed the CLA.

[imchairmanm]

Hey @javienc, thanks so much for the PR! I think a fix for the PostBin node has actually been merged into the main repo, so it should be included in the next release. I'm going to close this one for now since I think that it shoul make this workaround unnecessary, but please let me know if you think that's not the case.