docs: Use proper document titles

By making the first section header of a different type, rst interprets
it as a document title.
docs/EEPROM: Document the structure of the unique ID

Before, the EEPROM layout spec only referred to the protocol spec, which
make it harder to quickly look something up. Now, the unique ID
structure is shown in the figure for quick lookup, but for the exact
meaning it still refers to the protocol specification.