Update main readme after migration of mysql prototype to repository's root

[frouioui]

After the mysql prototype is merged into the repository's root, the main README will need to be updated. Issue #17 is highly related.

The README will need to host new informations concerning the technologies and tools that are being used. The SQL data models, the updated list of feature, and an updated list of command to run in order to get the Kubernetes cluster started.

[frouioui]

After testing out the cluster's startup with @meng2468 earlier, we concluded that a few more commands will need to be added to the current readme version:

• Install of jsonnet-bundler (both Mac and Linux)
• Install of yq (https://github.com/mikefarah/yq)
• Install of mysql and mysql-client (both Mac and Linux)
• Install of vtctlclient (using go get vitess.io/vitess/go/cmd/vtctlclient)