docs: rewrite README in plainer language

[CMaintz]

Went through the README so it reads well for someone skimming and still works as a reference.

• Status was out of date: .NET has a gate workflow behind the facade now, not just PHP. Also dropped a mention of a quality.yml that doesn't exist and fixed the templates/ link text (it's mise/).
• Plainer wording, no em-dashes, far less bold. Every table, command and claim is still there.