add notes regarding exporting/importing market data with lotus-shed

[nonsense]

This PR is adding steps on how to export/import a backup with all markets-related metadata, so that users who upgraded to a multi-service architecture and accepted storage deals, can continue to retrieve those deals correctly in case they rollback to a monolith architecture.

[filecorgi]

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docs/mine/lotus/split-markets-miners.md:

• A comma may be missing after the conjunctive/linking adverb ‘Currently’.

  ... subsystems in the lotus-miner process. Currently there are 4 subsystems, th...
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• An apostrophe may be missing.

  ...istinct types of lotus-miner nodes: The markets node - a lotus-miner process...
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• The preposition ‘for’ seems more likely in this position.

  ...ode - a lotus-miner process responsible to handling the storage market subsy...
                                             ^^
  

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  ...ode is started with configuration for a markets node, it includes a libp2p n...
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• The word “backup” is a noun. The verb is spelled with a space.

  ... the monolith miner process, you should backup your miner's metadata reposit...
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• Consider a shorter alternative to avoid wordiness.

  ...the LOTUS_BACKUP_BASE_PATH env variable in order to do that. # Splitting the...
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  ...ou need to create a config.toml for the markets node, and have it ready for ...
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• Possibly missing comma found.

  ...ve it ready for the next step. For more information see configuration usage ...
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  ...proving node on the same machine as the markets node, make sure that their l...
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• Did you mean: “By default,”?

  ...sure that their listeners do not clash. By default the lotus-miner API serve...
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• An apostrophe may be missing.

  ... you adjust the [Libp2p] section on the markets node accordingly - it needs ...
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  .... This performs a one-time setup of the markets node. Part of that setup inc...
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• This abbreviation for “identification” is spelled all-uppercase.

  ...f that setup includes updating the peer id in the miner actor by submitting ...
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  ...able! This command should be run on the markets miner instance host, as it i...
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  ...er instance host, as it is creating the markets miner instance repository, a...
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  ...aling/proving miner process without the markets subsystem Update your config...
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• Possibly missing comma found.

  ...oving miner process without the markets subsystem Update your config.toml an...
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  ...TH environment variable! # 6. Start the markets miner process with the marke...
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  ...tart the markets miner process with the markets subsystem # Interacting with...
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• If the ‘because’ clause is essential to the meaning, do not use a comma before the clause.

  ... interacting with only one miner process, because it has precedence over LOT...
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• An apostrophe may be missing.

  ...US_MINER_PATH. Now that you have both a markets miner process and a mining/s...
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• An apostrophe may be missing.

  ...following: Get the peer identity of the markets miner process Get a list of ...
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• Only proper nouns start with an uppercase character (there are exceptions for headlines).

  ...r identity of the markets miner process Get a list of storage deals from the...
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• An apostrophe may be missing.

  ...ss Get a list of storage deals from the markets miner process Get a list of ...
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• Only proper nouns start with an uppercase character (there are exceptions for headlines).

  ...ge deals from the markets miner process Get a list of sectors from the minin...
                                             ^^^
  

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  ...cly exposed, as we will be enabling the markets subsystem on it. In the mini...
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• Only proper nouns start with an uppercase character (there are exceptions for headlines).

  ...ml and set EnableMarkets option to true Move back the DAG store directory to...
                                             ^^^^
  

• An apostrophe may be missing.

  ...s it was changed to the identity of the markets node during the initialising...
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• An apostrophe may be missing.

  ...g/proving node, which now also runs the markets subsystem, i.e. currently al...
                                             ^^^^^^^