Add a bit of inline documentation to the Scan SOAC
Add a bit of inline documentation to the Scan SOAC

diku-dk/futhark,diku-dk/futhark,diku-dk/futhark,diku-dk/futhark,diku-dk/futhark,ihc/futhark,HIPERFIT/futhark,ihc/futhark,HIPERFIT/futhark,HIPERFIT/futhark,ihc/futhark