Update INSTALL.md to include local development instructions

[vadasambar]

I have built my gcp-stack image following the INSTALL.md

But it ends at Install part with TBD. I also tried out installing this using the crossplane repo's way (by running scripts under cluster/local/minikube.sh up) but there are not scripts under cluster/ folder.

Will running the built image as deployment do or is there any canonical/recommended way to install gcp-stack in my minikube?