Create additional blockchains using the avalanche-cli

[j-woodlee]

Is your feature request related to a problem? Please describe.
After following this process: https://docs.avax.network/build/subnet/hello-subnet I can't find any documentation related to creating additional blockchains within the same subnet.

Describe the solution you'd like
A couple lines added to the docs the demonstrate how to build, sign, and commit a 'create blockchain' transaction.

Describe alternatives you've considered
I see from the network runner docs, I might be able to use the ANR if I pass it a custom grpc endpoint. However, I haven't been able to get that to work. I am interested mainly in the avalanche-cli process where I commit the transaction to the network myself.

Additional context
I understand the concept of using the transaction sign and transaction commit functions within avalanche-cli, but as a noob I am in need of guidance in showing how to 1) construct the transaction file 2) sign transaction 3) commit transaction when it comes to creating a new blockchain. Thank you for the help!