[Tails-dev] Review doc/7747-persistent-volume-damage

I'm asking for a review only first, by people doing user support,
documentation, etc. to check for the relevance of this content.

branch: doc/7747-persistent-volume-damage
ticket: https://labs.riseup.net/code/issues/7747
        Document that physically removing the USB stick to stop Tails
        might damage the persistent volume

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sajolida