Added rst file for divergence functions.
Added rst file for divergence functions.

laijingtao/landlab,landlab/landlab,SiccarPoint/landlab,Carralex/landlab,laijingtao/landlab,landlab/landlab,Carralex/landlab,cmshobe/landlab,SiccarPoint/landlab,amandersillinois/landlab,ManuSchmi88/landlab,ManuSchmi88/landlab,RondaStrauch/landlab,Carralex/landlab,csherwood-usgs/landlab,cmshobe/landlab,csherwood-usgs/landlab,cmshobe/landlab,ManuSchmi88/landlab,landlab/landlab,RondaStrauch/landlab,RondaStrauch/landlab,amandersillinois/landlab