doc: add source-guide.md
doc: add source-guide.md

reuben/freshplayerplugin,Papapashu/freshplayerplugin,Papapashu/freshplayerplugin,grevutiu-gabriel/freshplayerplugin,grevutiu-gabriel/freshplayerplugin,reuben/freshplayerplugin,reuben/freshplayerplugin,Papapashu/freshplayerplugin