Add pre & post deployment command details to docs

[andrasbacsai]

• Pre-deployment commands (they are simple)
• Post-deployment commands: They could fail -> deployment will fail -> app won't be rolled back.

[tonven]

Hi. I have a question regarding pre & post deployment command. I have a command to run database migration script from nextjs app on my running supabase instance. The problem comes to choose which command I need to use. I thought that logically I need to use predeployment script. So it should create a new container, run migrations from it, and then, if there is no errors, deploy it. But as I understood, predeployment script is executed on existing container(correct me if I am wrong).
Because of this I need to run migration as a part of postdeployment command. But from your comment it will mean, that if migrations fail, it will still deploy a new container. Is this correct? Thank you for great product :)