Update index.md

From codes of geth we can know that evm is not a single entity. also from ethereumBook in chapter13:“When a transaction results in smart contract code execution, an EVM is instantiated with all the information required in relation to the current block being created and the specific transaction being processed. In particular”，"with each call resulting in another EVM being instantiated around the new target of the call. ",you can find it in 'https://github.com/ethereumbook/ethereumbook/blob/develop/13evm.asciidoc'

Author: cradle0fFilth

src/content/developers/docs/evm/index.md

@@ -4,7 +4,7 @@ description: An introduction to the Ethereum virtual machine and how it relates
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-The EVM’s physical instantiation can’t be described in the same way that one might point to a cloud or an ocean wave, but it does _exist_ as one single entity maintained by thousands of connected computers running an Ethereum client.
+The Ethereum Virtual Machine(EVM) is the runtime environment for smart contracts in Ethereum.Every time a transaction is executed, a new EVM instance is created to maintain a unique world state machine.
 
 The Ethereum protocol itself exists solely for the purpose of keeping the continuous, uninterrupted, and immutable operation of this special state machine. It's the environment in which all Ethereum accounts and smart contracts live. At any given block in the chain, Ethereum has one and only one 'canonical' state, and the EVM is what defines the rules for computing a new valid state from block to block.