Updated File Based Application documentation to include MSBuild Props instructions

[licon4812]

This pull request updates the documentation for using TUnit with file-based C# applications, adding new instructions for utilising MSBuild props files to simplify package management and test execution.

Enhancements to TUnit usage documentation:

• Added a new method for including TUnit via Directory.build.props files, with an example of the XML configuration.
• Introduced a new section on using MSBuild props files with single-file C# applications, including a step-by-step guide and a sample test script.

This relates to #2536