Add comprehensive documentation to README and package README

[Copilot]

The README lacked essential information for users to effectively adopt this template. Added complete documentation covering template usage, development setup, architecture, and CI/CD pipeline. Also created a package README for NuGet distribution.

Changes

• Template Usage: Step-by-step customization guide (namespaces, project metadata, badges)
• Development Prerequisites: SDK version (10.0.100), local vs Dev Container setup
• Folder Structure: Directory tree with explanations of build configuration files (Directory.Build.props, Directory.Packages.props, global.json)
• CI/CD Pipeline: Complete workflow breakdown:
  • Lint → Validate → Test (6 OS variants × 4 frameworks) → Pack (versioning strategy) → Publish (NuGet.org/GitHub Packages)
  • Trigger conditions and release process
  • Required secrets and variables
• Contributing Guidelines: Issue reporting, PR workflow, code style, testing requirements
• NuGet Package README: Created src/Sample.Core/README.md with usage examples for FizzBuzz and Counter, configured to be included in published packages

Expanded from 29 to 324 lines, organized with hierarchical sections for easy navigation.

Updated to .NET 10.0 SDK and framework support (10.0, 9.0, 8.0) by merging latest main branch.

• Fixes Add guide on README #100

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add guide on README</issue_title>
<issue_description>- [ ] How to use this template (change namespace and so on)

• Development (required SDK)
• Folder structure
• CI/CD guide
• Contribute
• Pack README on published library</issue_description>

<agent_instructions>If README will be huge, separete to another document.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Add guide on README #100

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (cd17b8a) to head (1a4f472).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #283   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines            4         4           
  Branches         1         1           
=========================================
  Hits             4         4           

Flag	Coverage Δ
Linux	100.00% <ø> (ø)
Windows	100.00% <ø> (ø)
macOS	100.00% <ø> (ø)
net48	100.00% <ø> (ø)
net8.0	100.00% <ø> (ø)
net9.0	100.00% <ø> (ø)

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[nogic1008]

@copilot

• Update to latest main branch
• Add README on package, not to guide

[Copilot]

@copilot

• Update to latest main branch
• Add README on package, not to guide

Done! Updated to latest main branch (b3f1b53) and added package README:

✅ Merged .NET 10.0 migration from main
✅ Updated README to reflect SDK 10.0.100 and framework support (.NET 10.0, 9.0, 8.0)
✅ Created src/Sample.Core/README.md with FizzBuzz and Counter usage examples
✅ Configured Sample.Core.csproj to include README in NuGet package
✅ Verified README is properly packaged in .nupkg file