feat: Create “A Tour of Vala” top-level page

Description

It will be a guided introduction, where the reader will see the overview of what the language.

Like a bite-sized version of the tutorial only taking time to explain unique concepts in the language with a bit more detail.

For example, everything from: Variables, foreach loops, arrays that you can append to, functions, classes, methods, signals, lambdas, async will all be covered.

However signals will be covered with more detailed instead of being briefly introduced.

Possible Solutions

The Swift Tour is a good resource to get some inspiration from: https://docs.swift.org/swift-book/documentation/the-swift-programming-language/guidedtour

Additional Info

No response