docs: Switch from master/slave in datasource readme
docs: Switch from master/slave in datasource readme

This also makes it slightly clearer that connections are arbitrarily named
CakeDC/cakephp,petteyg/cakephp,garethellis36/cakephp,ADmad/cakephp,petteyg/cakephp,tenkoma/cakephp,cakephp/cakephp,CakeDC/cakephp,garethellis36/cakephp,mvdriel/cakephp,garethellis36/cakephp,davidyell/cakephp,cakephp/cakephp,mvdriel/cakephp,cakephp/cakephp,dakota/cakephp,dakota/cakephp,cakephp/cakephp,dakota/cakephp,mvdriel/cakephp,garethellis36/cakephp,ndm2/cakephp,tenkoma/cakephp,CakeDC/cakephp,petteyg/cakephp,ndm2/cakephp,ADmad/cakephp,dakota/cakephp,petteyg/cakephp,davidyell/cakephp,ndm2/cakephp,tenkoma/cakephp,davidyell/cakephp,ADmad/cakephp,CakeDC/cakephp,ndm2/cakephp,mvdriel/cakephp,tenkoma/cakephp,ADmad/cakephp