The Declaration emphasizes the principles of liberty, equality, and fraternity (brotherhood) as fundamental rights of all citizens. While "fraternity" isn't a separately defined element like liberty and equality, it's implicitly woven throughout. The emphasis on the common good, the shared rights of all citizens, and the rejection of arbitrary privileges all contribute to the underlying notion of fraternity.
Therefore, there's no single "Decree of Fraternity," but the ideal of fraternity is a core component of the Declaration of the Rights of Man and of the Citizen, which formed the bedrock of the French Revolution's ideals. The pursuit of a more fraternal society, free from the inequalities and privileges of the Ancien Régime, was a driving force behind the revolution.