Deployment guide feedback missing GitHub steps

[shashivj]

Section heading: How to build an ABI project --> Step 2.
Documentation issue description: once submodule is added, the directory is empty. you have to run additional command, "git submodule update --init --recursive" to have the submodule populated with files.

https://aws-abi.s3.amazonaws.com/guide/cfn-abi-aws-reference-guide/how-to-build/index.html