Add Documentation for headless Building

[cpebble]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• New feature or enhancement
• UI change (please include screenshot!)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Internationalization and localization
• Other (please describe):

What is the new Documentation?

I had to build this without a GUI attached on our build server and I had to fumble my way through.

I wrote down my steps, and added a subheading in CONTRIBUTING.md.

Other information

I understand if changes are necessary before merging. I don't usually package dotnet sources, so please advise on what changes should be made

[cpebble]

I would like to note that the binary "feels" more stable when using
./build.sh --configuration Release --target PublishApp
However i wasn't able to get that running without changing

    Target GenerateSdkNuGet => _ => _
        .Description("Generate the DevToys SDK NuGet package")
        .DependsOn(SetVersion)
        .DependsOn(Restore)
        .DependsOn(Compile) # <----
        .Executes(() =>
        {

From CompileGenerators to Compile, as

[ERR] GenerateSdkNuGet: /usr/share/dotnet/sdk/8.0.106/Sdks/NuGet.Build.Tasks.Pack/buildCrossTargeting/NuGet.Build.Tasks.Pack.targets(221,5): error NU5026: The file '/home/cpj/work/external/DevToys/bin/Release/AnyCPU/DevToys.Api/net8.0/af-ZA/DevToys.Api.resources.dll' to be packed was not found on disk. [/home/cpj/work/external/DevToys/src/app/dev/DevToys.Api/DevToys.Api.csproj]

It seems a result of localization resources being cleaned in the first step