Add statements to documentation clarifying local/global time references

setup. The local time reference is the time of entry of the *first* primary particle of the event into the sensor. This means

that secondary particles created within the sensor inherit the local time reference from their parent particles in order to

have a uniform time reference in the sensor. It should be noted that Monte Carlo particles that start the local time frame on

different detectors do not necessarily have to belong to the same particle track.

different detectors do not necessarily have to belong to the same particle track. Few exceptions to these definitions exist and

are commented on in the corresponding module descriptions.

## Changing and accessing the geometry

Noise can be applied to the individual bins of the output pulse, drawn from a normal distribution.

The values stored in `PixelHit` depend on the Time-of-Arrival (ToA) and Time-over-Threshold (ToT) settings. If a ToA clock is defined, then `local_time` will be stored in ToA clock cycles, else in time units. If a ToT clock is defined, then `signal` will be the amount of ToT cycles the pulse is above the threshold, else it will be the integral of the amplified pulse.

The values stored in `PixelHit` depend on the Time-of-Arrival (ToA) and Time-over-Threshold (ToT) settings.

If a ToA clock is defined, then `local_time` will be stored in ToA clock cycles, else in time units. Using the parameter `sync_event_time`, this local time will be, in contrast to the framework's definition of local time stamps, aligned with the global time reference, optionally shifted by the value of the parameter `tdc_offset`.

If a ToT clock is defined, then `signal` will be the amount of ToT cycles the pulse is above the threshold, else it will be the integral of the amplified pulse.

Since the input pulse may have different polarity, it is important to set the threshold accordingly to a positive or negative value, otherwise it may not trigger at all.

If this behavior is not desired, the `ignore_polarity` parameter can be set to compare only the absolute values of the input and the threshold value.