Update tree.md
Update tree.md

Set onDelete='CASCADE' to delete the referencing entries.
lafourchette/DoctrineExtensions,birko/DoctrineExtensions,jmcclell/DoctrineExtensions,rubenrua/DoctrineExtensions,akd3vs/DoctrineExtensions,hhjcz/DoctrineExtensions,sroze/DoctrineExtensions,l3pp4rd/DoctrineExtensions,nirav-programmer/DoctrineExtensions,notrix/DoctrineExtensions,stof/DoctrineExtensions,cmfcmf/DoctrineExtensions,gadelkareem/DoctrineExtensions,pmishev/DoctrineExtensions,SocialbitGmbH/DoctrineExtensions,aramalipoor/DoctrineExtensions,blazarecki/DoctrineExtensions,edigu/DoctrineExtensions,tomazahlin/DoctrineExtensions,Engerim/DoctrineExtensions,eliberty/DoctrineExtensions,Preis24/DoctrineExtensions,teohhanhui/DoctrineExtensions,CiscoVE/DoctrineExtensions,anesse/DoctrineExtensions,bocharsky-bw/DoctrineExtensions,marc-j/DoctrineExtensions,Viburnum/DoctrineExtensions,lengpiseth/DoctrineExtensions,mablae/DoctrineExtensions,aplysie/DoctrineExtensions,Padam87/DoctrineExtensions,tyx/DoctrineExtensions,jeroendesloovere/DoctrineExtensions