try heading hierarchy

Author: davidekete

Intro-to-blockchain-and-ethereum/intro-to-blockchain/README.md

@@ -6,7 +6,7 @@ On public blockchains (some blockchains are private), identical copies of this l
 
 At a high level, three parts cooperate: an execution layer that deterministically turns transactions into state changes, a consensus mechanism that orders blocks and decides what becomes canonical, and data availability/state so everyone can fetch and verify the data. When these are aligned, immutability is the practical outcome and rewriting history becomes economically prohibitive.
 
-### Consensus mechanism
+## Consensus mechanism
 
 A consensus mechanism is how the network agrees on the next valid block. For example, **proof-of-stake**, where validators bond capital and can be slashed, and or **proof-of-work**, where miners prove computational effort.