Update contributing docs for adapter data path reasonings

[baltpeter]

Between tweaselORG/tracker-wiki#16, tweaselORG/tracker-wiki#7, and all the documentation PRs here, we have now established a pattern for how to document adapter data path reasonings.

The contributing section in the README needs to be updated accordingly:

TrackHAR/README.md

Line 162 in b219141

One way of doing that is by the property name. Some property names are obviously connected to one data type, e.g. a property named `screen_width` likely contains the screen width of the device. In other cases, the values are very obvious, e.g. `iOS` likely refers to the name of the operating system. In many cases, however, it is not that clear cut. You might recognize a property from specific honey data you planted, such as the longitude and latitude of a fake location which show up in the request data or the IDFA of the device that you know beforehand. In these cases, you need to publicly document your research showing how you reached the conclusion that a specific type of data is present in the request and refer to that research in the adapter via a permalink (we are currently working on a proper place for this, see [tweaselORG/meta#3](https://github.com/tweaselORG/meta/issues/3)).