Adapt documentation

kuksa_databroker/doc/behavior.md

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+# Runtime behavior and potential attacks
+The implementation of KUKSA databroker shall represent the latest value of a ```Datapoint```. Therefore the databroker always sets a ```timestamp``` for a ```Datapoint```. This means if a new value comes in it overwrites the older value. We opted for this behavior because a actuator/provider/application can have no access to a system time. For some use cases it could be interesting to provide a timestamp set by the actuator/provider/application. For this we added a so called source timestamp (short ```source_ts```) to the ```Datapoint``` class. This source timestamp is optional and per default set to None.
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+If an attacker gets an authorized connection to the databroker he can set the source_timestamp and overwrite the value with a new one. But for this he/she needs read and write access through JWT tokens. If a provider decides to work with ```source_ts``` of a ```Datapoint``` than it should be clear that they can be false/outdated.