update docs for severity options
update docs for severity options

muffato/public-plugins,andrewyatz/public-plugins,andrewyatz/public-plugins,andrewyatz/public-plugins,andrewyatz/public-plugins,muffato/public-plugins,Ensembl/public-plugins,Ensembl/public-plugins,Ensembl/public-plugins,muffato/public-plugins,muffato/public-plugins,andrewyatz/public-plugins