fix: update section 2 index pages (#977)

next/content/systems/_index.md

@@ -4,3 +4,13 @@ description: Filecoin Systems
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+In this section we are detailing all the system components one by one in increasing level of complexity and/or interdependence to other system components. The interaction of the components between each other is only briefly discussed where appropriate, but the overall workflow is given in the Introduction section. In particular, in this section we discuss:
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+- Filecoin Nodes: the different types of nodes that participate in the Filecoin Network, as well as important parts and processes that these nodes run, such as the key store and IPLD store, as well as the network interface to libp2p.
+- Files & Data: the data units of Filecoin, such as the Sectors and the Pieces.
+- Virtual Machine: the subcomponents of the Filecoin VM, such as the actors, i.e., the smart contracts that run on the Filecoin Blockchain, and the State Tree.
+- Blockchain: the main building blocks of the Filecoin blockchain, such as the structure of the Transaction and Block messages, the message pool,  as well as how nodes synchronise the blockchain when they first join the network.
+- Token: the components needed for a wallet.
+- Storage Mining: the details of storage mining, storage power consensus, and how storage miners prove storage (without going into details of proofs, which are discussed later).
+- Markets: the storage and retrieval markets, which are primarily processes that take place off-chain, but are very important for the smooth operation of the decentralised storage market.

next/content/systems/filecoin_blockchain/struct/_index.md

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 title: "Blocks"
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+---
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+The Block is the main unit of the Filecoin blockchain, as is also the case with most other blockchains. Block messages are directly linked with Tipsets, which are groups of Block messages as detailed later on in this section. In the following we discuss the main structure of a Block message and the process of validating Block messages in the Filecoin blockchain.

next/content/systems/filecoin_blockchain/struct/block/_index.md

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 # Block
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-The Block is a unit of the Filecoin blockchain.
 
 A block header contains information relevant to a particular point in time over which the network may achieve consensus.
 

next/content/systems/filecoin_nodes/_index.md

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 dashboardAudit: 1
 dashboardState: incomplete
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+This section is providing all the details needed in order to implement any of the different Filecoin Nodes. Although node types in the Filecoin blockchain are less strictly defined than in other blockchains, there are still a few different types of nodes each with its own features and characteristics.
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+In this section we also discuss issues related to storage of system files in Filecoin nodes. Note that by storage in this section we do not refer to the storage that a node is commiting for mining in the network, but rather the local storage that it needs to have available for keys and IPLD data among other things.
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+The network interface and how nodes connect with each other and interact using libp2p, as well as how to set the node's clock is also discussed here.