add Cosmovisor.service instructions

[TaxiStake]

source documentation: https://docs.osmosis.zone/networks/join-mainnet#update-cosmovisor-to-v10

Closes: #XXX

What is the purpose of the change

Add a description of the overall background and high level changes that this PR introduces

Small documentation addition for cosmovisor steps for v12 upgrade.

Add cosmovisor.service steps

source documentation: https://docs.osmosis.zone/networks/join-mainnet#update-cosmovisor-to-v10

Brief Changelog

• Add cosmovisor.service steps

[czarcas7ic]

Hey, thank you for the contribution! IMO, the upgrade instructions that live in the repo should simply be bare minimum. If users want to improve their setups (creating auto restarting services etc), then they should be checking out the docs site. I believe this currently lives in the docs site. If others disagree with me, then at the very least we should move this addition to the "## First Time Cosmovisor Setup" section. Either way is fine with me.

Thanks again!

[github-actions[bot]]

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