* Update README to use releases-stability URL

Change https://docs.openzeppelin.com/contracts/api-stability to https://docs.openzeppelin.com/contracts/releases-stability (even though it redirects)

* Update README to include CLI as dev env

Add OpenZeppelin CLI to list of development environments

* Update README to use releases-stability URL

Change https://docs.openzeppelin.com/contracts/api-stability to https://docs.openzeppelin.com/contracts/releases-stability (even though it redirects)