Document the complete test-suite addition workflow

[sylvesterkaczmarek]

Summary

• add a concise checklist covering test descriptions, generated patterns and references, implementation files, build registration, and regenerated sources
• direct test and benchmark files to their current Include and Source subdirectories
• link the existing pattern-generation example and generation instructions

Context

The current instructions still point contributors to Include/MyClass.h and Source/MyClass.cpp, and they omit several required integration steps. The repository now keeps tests and benchmarks in separate subdirectories and registers implementations in Testing/CMakeLists.txt.

Fixes #259.

Validation

• git diff --check
• verified that Testing/PatternGeneration/Example.py, the documented source directories, and the referenced CMake file exist on main
• verified that the internal README heading link targets the existing generation section

Documentation-only change. No code tests were run.

[sylvesterkaczmarek]

Refreshed this PR onto current main today. It is mergeable, with no failing/error checks or outstanding changes-requested reviews. This has been quiet since August. Could a maintainer please review it when convenient, or let me know if anything further is needed?