PowerShell examples added to automated bibisecting wiki article

[Ilmari Lauhakangas]

Check it out, ya'll: 
https://wiki.documentfoundation.org/QA/Bibisect/Automation#Automating_bisecting_with_scripts

I thought it would be nice to use 'git bisect run' also with native 
Windows git, so I created PowerShell versions of the Bash scripts.

Last month I had added a couple of additional Bash examples, done some 
cleanups and expanded the explanations.

Ilmari