Enhance documentation for Nunjucks variables

[gerteck]

Add docs for basic usage and escaping syntax

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:

Overview of changes:

Add some basic variable syntax into the user guide so it is easier to get started without already being familiar with nunjucks and their templates.

No particular issue, but found the user guide lacking in this aspect as in what would have been useful to me when adding feature that supports nunjucks.

Anything you'd like to highlight/discuss:

Testing instructions:

Proposed commit message: (wrap lines at 72 characters)

Enhance docs for Nunjucks variables

Add docs for basic usage and escaping syntax

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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

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Reviewer checklist:

Indicate the SEMVER impact of the PR:

• Major (when you make incompatible API changes)
• Minor (when you add functionality in a backward compatible manner)
• Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.65%. Comparing base (dc7263e) to head (c165ee1).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #2764    +/-   ##
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  Coverage   61.65%   61.65%            
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  Files         130      130            
  Lines        7167     7167            
  Branches     1573     1505    -68     
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  Hits         4419     4419            
+ Misses       2685     2558   -127     
- Partials       63      190   +127     

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[Copilot]

Pull request overview

This pull request enhances the Nunjucks variables documentation by adding introductory content to help users get started with basic variable usage and syntax escaping. The changes provide essential information that was previously missing, making the documentation more accessible to users unfamiliar with Nunjucks.

• Adds a "Basic Usage of Variables" section with a practical example of defining and using variables
• Introduces an "Escaping Nunjucks Syntax" subsection explaining how to display Nunjucks syntax literally
• Provides guidance on variable naming conventions and case sensitivity

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[gerteck]

Updated documentation here: https://deploy-preview-2764--markbind-master.netlify.app/userguide/reusingcontents#basic-usage-of-variables

[github-actions]

@gerteck Each PR must have a SEMVER impact label, please remember to label the PR properly.