README.md steps for adding screens

[barnettwilliam]

In the readme it would be useful to include a summary of the steps for adding a module's screens. In particular to indicate that relevant entries need to be added to techui-support.yaml for screens to be picked up when running techuip-builder.

[barnettwilliam]

A note on where to find auogenerated screens from generic iocs would be helpful, inside container /epics/opi mapped to ioc-[name]/opi/auto-generated that can be used as a starting point for customised screens