Add docs for custom layer properties
Add docs for custom layer properties

ger-benjamin/ngeo,Jenselme/ngeo,balpreetspankaj/ngeo,mygu/ngeo,Jenselme/ngeo,Jenselme/ngeo,Jenselme/ngeo,mygu/ngeo,balpreetspankaj/ngeo,camptocamp/ngeo,elemoine/ngeo,gberaudo/ngeo,kalbermattenm/ngeo,adube/ngeo,elemoine/ngeo,ger-benjamin/ngeo,elemoine/ngeo,pgiraud/ngeo,kalbermattenm/ngeo,tsauerwein/ngeo,camptocamp/ngeo,ger-benjamin/ngeo,pgiraud/ngeo,camptocamp/ngeo,balpreetspankaj/ngeo,mygu/ngeo,gberaudo/ngeo,adube/ngeo,pgiraud/ngeo,kalbermattenm/ngeo,adube/ngeo,tsauerwein/ngeo,gberaudo/ngeo,camptocamp/ngeo,camptocamp/ngeo,adube/ngeo