[Problem] Testnet node hosting guilde is not updated

The docs needs to be updated accordingly with the testnet upgrade from `v0.6.*` to `v0.7.*`

1. run 0.6.0-testnet until block `1553700`
1. upgrade to 0.7.0-rc1-testnet  and update ~/.cronos/config/app.toml ([link](https://github.com/crypto-org-chain/cronos-testnets/blob/main/cronostestnet_338-3/app.toml)) and resume to sync from block `1553700`