Expand guide to include usage of the browser developer tools.

The guide currently does mention the browser developer tools but doesn't go into it too much. Working with the developers tools is however a valuable skill when working on test automation for websites.

Things to include:

• Basic inspect element usage.
• Selector validation (is my selector unique and selecting the right element.
• Basic CSS manipulation in order to highlight things on page.
• Possibly some browser extensions that are often used to aid in selector creation.