Update learning-powershell.md
Update learning-powershell.md

Fixing typos and "More Reading" section.

JamesWTruher/PowerShell-1,jsoref/PowerShell,KarolKaczmarek/PowerShell,KarolKaczmarek/PowerShell,kmosher/PowerShell,kmosher/PowerShell,PaulHigin/PowerShell,PaulHigin/PowerShell,bmanikm/PowerShell,bingbing8/PowerShell,bingbing8/PowerShell,kmosher/PowerShell,jsoref/PowerShell,daxian-dbw/PowerShell,bingbing8/PowerShell,kmosher/PowerShell,TravisEz13/PowerShell,bmanikm/PowerShell,KarolKaczmarek/PowerShell,daxian-dbw/PowerShell,KarolKaczmarek/PowerShell,bingbing8/PowerShell,jsoref/PowerShell,jsoref/PowerShell,TravisEz13/PowerShell,PaulHigin/PowerShell,bingbing8/PowerShell,JamesWTruher/PowerShell-1,daxian-dbw/PowerShell,JamesWTruher/PowerShell-1,bmanikm/PowerShell,KarolKaczmarek/PowerShell,bmanikm/PowerShell,TravisEz13/PowerShell,JamesWTruher/PowerShell-1,kmosher/PowerShell,bmanikm/PowerShell,TravisEz13/PowerShell,PaulHigin/PowerShell,jsoref/PowerShell,daxian-dbw/PowerShell