Broken link in the issue form

[bonanitech]

Current Behavior

As mentioned in #1450 (comment), the 'handbook' link at the end of the issue form is broken.

Expected Behavior

No response

Steps To Reproduce

Create a new issue in this repository and click on the 'handbook' link at the end of the issue form.

It will return this error message.

Environment

• Dashboard version:
• Node-RED version:
• Node.js version:
• npm version:
• Platform/OS:
• Browser:

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I have provided an initial effort estimate