templates/portfolio.html: Fix closing H5 tag
templates/portfolio.html: Link NetControl project to its page at GitHub
portfolio: Add description from course "Intro to AI"

The template from `project-sample.html` has been taken as an example for
now, but it will need changing so that it displays info about the course,
such as contents, university, statement of accomplishment, etc.
templates/portfolio.html: Add image to NetControl
templates/intro_ai.html: Customize "Intro to Artificial Intelligence"

The existing templates and styles weren't suitable for what I want, so
this commit needs to add custom CSS to `style.css`.
templates, style.css: Aesthetic changes, mainly concerning text size

I couldn't help seeing everything a bit too small. The previous default
text size of all the paragraphs was 8px and this commit changes it to 10px.