Update README PluralSight links

[Asafima]

This section in the README file has wrong links to old urls in PluralSight. After some digging I found the right courses.

From the README file:

Goals

The goal of this repository is to provide a basic solution structure that can be used to build Domain-Driven Design (DDD)-based or simply well-factored, SOLID applications using .NET Core. Learn more about these topics here:

SOLID Principles for C# Developers SOLID Principles of Object Oriented Design (the original, longer course) Domain-Driven Design Fundamentals

The wrong links are the first and second, SOLID Principles of Object Oriented Design Domain-Driven Design Fundamentals

I'll add a fix.