docs: describe clib_time monotonic timebase support
docs: describe clib_time monotonic timebase support

Type: docs

Signed-off-by: Dave Barach <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@barachs.net>
Change-Id: I5b27d8b945472388498a4afc4be8dd868bb45ac3

FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp