doc: add build wg info to releases.md
Given the issues faced when preparing the security release tonight, I think it is necessary to document the expectations and reality faced from the Build Working Group. I am hopeful that defining the relationship between the releasers and the all-volunteer WG will help to try and avert last-minute-dashes in the future.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
documentation is changed or added -
commit message follows commit guidelines