usage: create doc to guide user build custom version of the toolkit

e.g:
```bash
docker build \
  --build-arg UBUNTU_VERSION=22.04 \
  --build-arg PYTHON_VERSION=3.11.3 \
  --build-arg ANSIBLE_VERSION=2.16.4 \
  --build-arg TERRAFORM_VERSION=1.7.4 \
  --build-arg KUBECTL_VERSION=1.29.2 \
  --build-arg HELM_VERSION=3.14.2 \
  --build-arg AWSCLI_VERSION=2.15.24 \
  -t custom-docker-image:latest .
```