Update FC design guidelines

[ot0tot]

Creating draft PR so @haslinghuis doesn't think I dropped the ball 😅

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This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs within a week.

[haslinghuis]

@ot0tot - please explain SPI 1 DMA limitations of F4 processors in F4 sections a bit more.

[nerdCopter]

can we undraft and merge? @ot0tot , any additions? i would like this available after potential merging of:

• https://github.com/betaflight/config/pull/458
• https://github.com/betaflight/betaflight.com/pull/427