Fix etcher docs

[SteveMicroNova]

During some support cases, the best course of action is to reflash your pi, which we have instructions for here

Balena Etcher no longer works with our images on windows, it errors out at the end on the verification step and leaves the amplipi in an unusable state. While testing these same images with an older version of Balena that I had installed, they worked just fine. This means we need to gate the version number in the docs somehow (or make our images actually work with the modern version, but linking to a different version of etcher seems much easier on our part)