Examples in README expanded with cat dog classifier link and short classifier code example

[Nelias]

Description

Added another live example of Brain.js in action

Motivation and Context

This is the result of a discussion here: https://github.com/BrainJS/brain.js-examples/pull/1

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Author's Checklist:

• [x] My code focuses on the main motivation and avoids scope creep.
• [x] My code passes current tests and adds new tests where possible.
• [x] My code is SOLID and DRY.
• [x] I have updated the documentation as needed.

Reviewer's Checklist:

• [ ] I kept my comments to the author positive, specific, and productive.
• [ ] I tested the code and didn't find any new problems.
• [ ] I think the motivation is good for the project.
• [ ] I think the code works to satisfies the motivation.