Adds a section for user namespace mappings
Adds a section for user namespace mappings

Signed-off-by: Mrunal Patel <d389837b018b67489df74a2c5f0aca13aaed44b6@gmail.com>

zenlinTechnofreak/specs,haijunTan/specs,runcom/specs,jonboulle/specs,opencontainers/runtime-spec,ChengTiesheng/specs,dustymabe/specs,wking/opencontainer-runtime-spec,opencontainers/specs,hqhq/runtime-spec,kensipe/specs,philips/specs,HardikDR/specs,vbatts/specs,talwai/specs,rootfs/specs,laijs/specs,marcosnils/specs,cloudfoundry-incubator/specs,hqhq/specs,wangkirin/specs,wking/opencontainer-specs,vishh/specs,sladage/specs,gao-feng/specs,ujuc/specs,LK4D4/specs,jhjeong-kr/specs,navidshaikh/specs,mheon/specs