Re-add Mycelium details to references > networks

[jsoares]

Mycelium was rebooted this week (though currently halted, will reset tomorrow). Let's re-add it to the networks page.

[linear]

DOC-13 Re-add Mycelium details to references > networks

[jsoares]

Should be fine to just resurface the content in https://github.com/consensus-shipyard/docs/blob/97af93a99d776c42488d80a4b7bb76ae4d9f5bd9/reference/networks.md, updating the subnet ID and chain ID.