message: doc: add link to the migration guide for mirana
diff: @@ -33,7 +33,9 @@ Nervos CKB is released under the terms of the MIT license. See [COPYING](COPYING
  ## Join a Network
  - Mainnet Mirana: Use the [latest release](https://github.com/nervosnetwork/ckb/releases/latest) and run `ckb init --chain mainnet` to initialize the node.
  + - Mirana is active since the epoch 5414, see the [migration guide](https://github.com/jordanmack/nervos-ckb2021-hard-fork-migration-guide) to upgrade from Lina.
  - Testnet Pudge: Use the [latest release](https://github.com/nervosnetwork/ckb/releases/latest) and run `ckb init --chain testnet` to initialize the node.
  + - Pudge is active since the epoch 3113.
  See more networks to join in the [wiki](https://github.com/nervosnetwork/ckb/wiki/Chains).
  