Add steps for installing git to the Readme because KlakNDI is a git package dependency

[hybridherbst]

Currently, users need to install git (https://git-scm.com/downloads) so that the modified KlakNDI package can be downloaded.
Otherwise, they receive this warning:

We should

• either include steps for how to set this up in the Readme
• or remove the need for installing git by releasing the modified KlakNDI package on a registry (e.g. under a different scope on OpenUPM).