Updated Quickstart with ARM32 & AARCH64

Added instructions for ARM 32 bit (Emulation and BeagleBone Enhanced)
and AARCH64 - ARM 64bit (Emulation).

v2 : Corrected path discrepancy.

v3 : Corrected qemu-run command.

v4 : Nested RPi4 & Rcar under AARCH 64.

Bug-AGL: [SPEC-3633]

Signed-off-by: Shankho Boron Ghosh <shankhoghosh123@gmail.com>
Change-Id: I7a031138091620568798568921305c43c00e219b
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/25623
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>