Add a safety note on using the new delete rules.
Add a safety note on using the new delete rules.

aszwemin/mongoengine,conversocial/mongoengine,9nix00/mongoengine,ConsumerPhysics/mongoengine,Davidrjx/mongoengine,MRigal/mongoengine,colinhowe/mongoengine,gmacon/mongoengine,MongoEngine/mongoengine,cogniteev/mongoengine,starsirius/mongoengine,prijindal/mongoengine,noirbizarre/mongoengine,losintikfos/mongoengine,Multiposting/mongoengine,khallaghi/mongoengine,eli-b/mongoengine,jimmyshen/mongoengine,DavidBord/mongoengine,ProgressivePlanning/mongoengine,Davidrjx/mongoengine,larsbutler/mongoengine,nicolascine/mongoengine,MakerReduxCorp/mongoengine,MakerReduxCorp/mongoengine,ContextLogic/mongoengine,blaggacao/mongoengine,reallistic/mongoengine,WingGao/mongoengine,iandd0824/mongoengine,Catstyle/mongoengine,closeio/mongoengine,elephanter/mongoengine,yarneo/mongoengine,gavincabbage/mongoengine,touilleMan/mongoengine,nathanial/mongoengine,hmarr/mongoengine,ms5/mongoengine,cogniteev/mongoengine,sourcelair/mongoengine,newvem/mongoengine,depop/mongoengine-stripped,RussellLuo/mongoengine,muhammad-ammar/mongoengine,ContextLogic/mongoengine,KarimAllah/mongoengine