Add TOC to README
Add TOC to README

[ci skip]
openmhealth/shimmer,Marc-Calis/shimmer,Marc-Calis/shimmer,Marc-Calis/shimmer,smalldatalab/omh-shims,openmhealth/shimmer,smalldatalab/omh-shims,smalldatalab/omh-shims,openmhealth/shimmer,openmhealth/shimmer,Marc-Calis/shimmer,smalldatalab/omh-shims