[Docs] Add Release Notes for 20.08
[Docs] Add Release Notes for 20.08

Resolves: LE-14713
Change-Id: Ia60778aaf94ba6a2094d9a840bf4fb535d6bc379

legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af