Add workflow/mapping.md to docs [skip ci]
Add workflow/mapping.md to docs [skip ci]

- explain mapping concept
- describes mapping.json format
- overview function to work wiht mapping.json files from PowerShellGitHubDev.psm1
bingbing8/PowerShell,PaulHigin/PowerShell,bmanikm/PowerShell,jsoref/PowerShell,daxian-dbw/PowerShell,jsoref/PowerShell,KarolKaczmarek/PowerShell,KarolKaczmarek/PowerShell,kmosher/PowerShell,daxian-dbw/PowerShell,bmanikm/PowerShell,KarolKaczmarek/PowerShell,TravisEz13/PowerShell,kmosher/PowerShell,KarolKaczmarek/PowerShell,TravisEz13/PowerShell,jsoref/PowerShell,bmanikm/PowerShell,daxian-dbw/PowerShell,bingbing8/PowerShell,kmosher/PowerShell,bingbing8/PowerShell,PaulHigin/PowerShell,bmanikm/PowerShell,jsoref/PowerShell,TravisEz13/PowerShell,JamesWTruher/PowerShell-1,kmosher/PowerShell,bingbing8/PowerShell,KarolKaczmarek/PowerShell,JamesWTruher/PowerShell-1,daxian-dbw/PowerShell,kmosher/PowerShell,JamesWTruher/PowerShell-1,jsoref/PowerShell,JamesWTruher/PowerShell-1,PaulHigin/PowerShell,bingbing8/PowerShell,TravisEz13/PowerShell,bmanikm/PowerShell,PaulHigin/PowerShell