release notes: Tweak the "FSFS f8 is new" bits in the intro.
* staging/docs/release-notes/1.10.html (#compatibility): Use the 'notice' box style to make the warning visible and to make it harder for us to forget to remove it when the time comes. Also merge the "do not upgrade" language from the existing notice box in #lz4. (#new-feature-compatibility-table): LZ4 storage requires 1.10 libraries. . We may be able to make it more obvious that 1.10's default FSFS format has been bumped: after GA, when the notices have been removed, #fsfs-format8 will be the only place that spells that out.