README: document how to install and run tracker and tracker-miners in a prefix
The README tells developers to build and install Tracker into /usr. This is bad advice that could result in them breaking their operating system.
We should instead document how to build, install and test Tracker and tracker-miners inside a custom prefix or a virtual machine.
The Tracker README should also point conspicuously to the tracker-miners.git README as most developers will actually want to build tracker-miners and include tracker.git as a subproject.