Add information about which Vanadium settings can safely deviate from defaults

[An-anonymous-coder]

In the Web browsing section of the Usage guide, it discusses how Vanadium is following the same school of thought as the Tor Browser regarding fingerprinting (i.e. blending into the crowd). Vanadium already has the same fingerprint when installed on devices of the same model. However, like Tor Browser, Vanadium lacks any explicit documentation regarding which settings the user can change without deviating from that baseline fingerprint. For example, each site setting you set to block by default can be used as a fingerprinting metric by measuring how quickly the permission is denied after requesting (which would be instantly, in this case). Permissions that are/aren't allowed to be changed should be clearly laid out to avoid accidental fingerprint changes.