[README] Document generic builders and matchers
[README] Document generic builders and matchers

mjarvis/Mockingjay,zachwaugh/Mockingjay,nwest/Mockingjay,nghialv/Mockingjay,felixclack/Mockingjay,mjarvis/Mockingjay,mjarvis/Mockingjay,kylef/Mockingjay,felixclack/Mockingjay,kylef/Mockingjay,nghialv/Mockingjay,mogstad/Mockingjay,zachwaugh/Mockingjay,nghialv/Mockingjay,mogstad/Mockingjay,nwest/Mockingjay