* Update device_tracker.fritz.markdown
Added zlib1g-dev, which is needed to link lxml. Rephrased to make clear that one either needs to install lxml from a repository or build it from sources.
* Fix name
In addition to the added packages, it is necessary to install lxml within the virtual environment if AiO install has been chosen (I did not verify with other installs). Otherwise HASS will not start and not give any error messages when device_tracker with Fritz is used.
Without it fritzconnection might not be able to install correctly on low-end machines (e.g. Raspberry Pi) due to running out of resources while trying to compile lxml via pip3.
