Add usage page for invoking Pester

[fflaten]

Checklist

• [X] Issue has a meaningful title
• [X] I have searched the existing issues. See issues

Summary of the request

There seems to be very little documentation on actually invoking Pester-tests, only how to write and structure Ex.

• Using Invoke-Pester with simple and advanced configuration
• Using filters (#242)
• Interactive execution
• Debugging?
• Caution/Note-mention of experimental vscode extension (#197)?

Suggested section

Usage or Introduction after installation.

[fflaten]

Inspiration: https://www.sapien.com/blog/2016/06/15/invoke-pester-run-selected-tests/

[fflaten]

Quick start should also link to Invoke-Pester