lba_problem: Remove redundant string formatting.
lba_problem: problematic_block: Say what argument `lba` means.

The determination/differentiation between sectors and numbers is confusing,
especially when you are scared to death that your drive is dying.
lba_problem: Add instructions on finding the initial sector of a partition.
lba_problem: Add docstring for whole program.
lba_problem: Remove garbage lines at the end of the file.

They are of no purpose to other people and the example of how to "fix" a
defective sector is already in the main documentation of the module.