We didn't specify that the db user needs the right to create
temporary tables before.
That's why the migration will fail on most installations.
This commits removes the "TEMPORARY" from the migration
and changes the documentation to include the necessary rights for the future.
When looking up the granted permissions for users in MySQL using `show grants for 'git'@'localhost';` it shows the permissions in this order regardless of how you enter them. Changing so that comparing your actual permissions vs. what installation guide says is easier.
