[WIP][TASK] Added chapter on LTS to LTS upgrade

Change-Id: I6597323f7b60bee047c6d5a679d0e0a7c7e8fb3c
Updated the 'Troubleshooting' section

Change-Id: I3a5da579d6d0654660004e69ba08d94cdb7286b6
Simplified and updated Quick Install chapter

Change-Id: Ide2940b6ae42c3b99d36b24c950dad100e254fb3
Updated the "In depth" section

Change-Id: I05d00e16e634064cd0a46c233124c30d10e1e17e