Updated Upgrade and Troubleshoot instructions

I have updated the Upgrade.md and the Troubleshoot.md so that people run into less problems when upgrading Baikal. 
In the Upgrade.md i have just changed the order of commands because when you move the specific folder on the command line after you have applied correct user:group and permissions it can happen that Baikal cant read ENABLE_INSTALL and refuses to work, although the file exists.

I have also updated the Troubleshoot.md to tell people how to use the composer (ihave never worked with that before), but this only works on the command line. Maybe it would be a good idea to extend that for people who are using Baikal on a shared hosting account.