🧰 Docs: Troubleshooting common build/restore issues

[jongalloway]

Collect frequent stumbling blocks into a small Troubleshooting section.

Scope

• Add a Troubleshooting section to the root README.md or doc/development-guide.md
• Cover:
  • .NET SDK version mismatches
  • NuGet feeds (using NuGet.Config and central Directory.Packages.props)
  • Docker dotnet restore tips (copy props/feeds early)
• Keep it concise with links to detailed docs

Acceptance Criteria

• New contributors can quickly self-unblock common restore/build problems

Labels: docs, good first issue