[boost] Update request to Boost Discussion Policy maintainers

Folks, May I request to update the "Effective Posting" section of the policy at: http://www.boost.org/community/policy.html#effective adding the following new sub-section as first: """ Use Sensible Subject Please make sure that your postings have a meaningful subject line that is related to the contents of your mail. Many people use this to help determine which posts to read and which to ignore when they're operating under time constraints. """ Best regards, -- Mateusz Loskot, http://mateusz.loskot.net