[boost] 1.75 schedule reminder

A reminder that Oct 21 was the cutoff date for new library additions, and the upcoming deadlines are - Oct 28: Boost 1.75.0 closed for major changes - Nov 4: Boost 1.75.0 closed for beta - Nov 11: Boost 1.75.0 beta - Dec 2: Boost 1.75.0 closed for release - Dec 9: Boost 1.75.0 release (See the calendar at https://www.boost.org/development/index.html.)