Port the old Database Restore documentation to 1.8

[euantorano]

The old 1.6 documentation has a guide on restoring a MyBB database. This should be updated for 1.6 and should be fleshed out a little (with screenshots of the restore process within phpMyAdmin for example).

Also, the restore process should be described for other database management systems such as PostgreSQL.

[AndreRl]

I think this will be beneficial now more than ever as IcyBoards is closing down and this is what's basically required. I could probably get this done for PhpMyAdmin, PgAdmin and SSH. Opinion? @euantorano

[andrewjs18]

sure, submit a PR and we'll check it out.

[AndreRl]

This issue should be marked as closed.