update readme and fix CI problem with .NET SDK version

[chtenb]

Fixes #102

[Copilot]

Pull Request Overview

This PR updates the README documentation and fixes CI issues by setting the .NET SDK version to 8.0.0. Additionally, minor comment formatting adjustments and new build targets have been introduced to improve code consistency and workflow setup.

• Updated CI workflows to use actions/setup-dotnet@v4 with .NET 8.0 SDK.
• Updated global.json to specify the .NET SDK version as 8.0.0.
• Made comment formatting improvements and added a tutorial width check in the justfile.

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
justfile	Added a new target (check-tutorial-width) using awk to enforce a maximum line length for Tutorial.cs.
global.json	Updated the .NET SDK version to 8.0.0.
Rubjerg.Graphviz.Test/Tutorial.cs	Improved comment formatting; modified SVG output filename in layout tests.
README.md & README-src.md	Revised wording and formatting for clarity regarding precompiled binaries and dependencies.
.github/workflows/*	Upgraded workflow steps to use actions/setup-dotnet@v4 and standardized .NET SDK version configuration.
.editorconfig	Added settings for Tutorial.cs to enforce a max line length of 100 characters.

Comments suppressed due to low confidence (2)

Rubjerg.Graphviz.Test/Tutorial.cs:79

• Ensure that renaming the SVG output file from '/dot_out.svg' to '/dot.svg' is intentional and that any dependent tests or file references have been updated accordingly.

root.ToSvgFile(TestContext.CurrentContext.TestDirectory + "/dot.svg");

.editorconfig:215

• [nitpick] Confirm that the max_line_length of 100 for Tutorial.cs aligns with the project's overall style guidelines and code readability standards.

max_line_length = 100