Document cyclical error in include in UG

[yucheng11122017]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Documents #2177

Overview of changes:
Added a warning about the cyclical error in includes when variables have the same name. Included suggested solution for this bug.

Anything you'd like to highlight/discuss:

Testing instructions:

Proposed commit message: (wrap lines at 72 characters)
Document cyclical error in include in UG

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

[damithc]

As this is a rare case (i.e., most users will not need to know about it), we should present it in a way most readers are not forced to read it but they can locate this information when they need to. Any ideas?
Perhaps a collapsed panel with a heading like A caveat, if you are recursive includes ... ?

[tlylt]

Thank you @yucheng11122017 for taking this up. Could we:

• add the explanation mentioned in Using include inside include results in cyclic references #2177 (comment) before the new panel to improve the current description, such that devs like yourself understand the rationale for such design
• construct an "MVP" example such that we show the cause, the error (which you have already included), and the resolution (which is missing)

[tlylt]

LGTM, fixed a typo and added line numbers for consistency within the panel.