Issue585document114multipleRDSR

Ref #114 to document imports from event level cumulative RDSRs. The docs are issue #585

Any comments welcome:

Main doc: http://docs.openrem.org/en/issue585document114multiplerdsr/import_multirdsr.html

Link from troubleshooting: http://docs.openrem.org/en/issue585document114multiplerdsr/troubleshooting.html