try heading hierachy

Author: davidekete

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

@@ -10,17 +10,17 @@ At a high level, three parts cooperate: an execution layer that deterministicall
 
 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.
 
-### Execution Layer
+## Execution Layer
 
 The execution layer defines how transactions are interpreted and applied to state, step by step, the same way on every node. For example, on EVM chains (Ethereum and many L2s), contracts compile to EVM bytecode.
 
 Note: Execution is separate from consensus; a network can change how it reaches agreement without changing how code runs, and vice versa.
 
-### State changes
+## State changes
 
 Users submit signed transactions that describe intended changes (transfer value, call a contract). Nodes execute these deterministically and, if valid, include them in blocks that extend the chain.
 
-### Immutability
+## Immutability
 
 Immutability isn’t “forbidden by code”; it’s economically enforced. On Ethereum, blocks become finalized when ≈ two-thirds of staked validators attest to the relevant checkpoints. Reverting a finalized block would require creating conflicting finality—an act that implies slashing at least one-third of the total staked ETH. With roughly ~35–36 million ETH staked today, that’s on the order of ≥11–12 million ETH at risk, which makes rewriting finalized history prohibitively costly.