Have all initial flashing docs add a note that disconnecting CMOS will put system clock in 1970

[tlaurion]

https://docs.dasharo.com/unified/novacustom/initial-deployment/#installing-dasharo

refs:

• key-init: force user to change time if <2024, give warnings on key import errors linuxboot/heads#1776 (comment) (and fix when PR merged for Heads fro that commit forward)
• long discussion with typical end user, leading to PR. He followed the Dasharo docs: https://matrix.to/#/!pAlHOfxQNPXOgFGTmo:matrix.org/$7RD8BU9vo8DzV3NEMo21bYxfa6U2P0V9GuqS-tgM9Ys?via=matrix.org&via=nitro.chat&via=envs.net

[macpijan]

@BeataZdunczyk Can we please schedule that? Should be enough to add a note as suggested.