classes/updatehub-image: Improve documentation
classes/updatehub-image: Improve documentation

- fix service name spelling, basically s/updatehub/UpdateHub/
- add information about the use of product id inside the distro
- rework line split to better use of line space (now splits on column 100)

Signed-off-by: Otavio Salvador <1d31b11c1b92bf5d043d36edfe7174db39a6b891@ossystems.com.br>

UpdateHub/meta-updatehub,UpdateHub/meta-updatehub,UpdateHub/meta-updatehub