update `scfm.pdf`

[achubaty]

this overview document is dated 2018, and needs to be updated:

• output html instead of pdf and link the intermediate md file as README;
• "this version of the module considers lighning-caused fires only" is a bit of an inaccurate word choice. As we can consider human caused fires, but we don't by default, as we can't recreate the spatial patterns as accurately;
• It makes no mention of "reporting" objects, which is noteworthy only because it has the option to pass studyAreaReporting, which is designed to reduce edge effect bias;
• There is now a more rigorous treatment of the reporting around fires that spread across interior edges (between polygons). Its a lot of detail but I suppose this is where it would be included;
• missing description of scfmDiagnostics;