Improve README

The current README is slightly vague in some areas and is missing a step to be able to start using techui-builder to generate screens:

1. The techui-support repo needs to be added as a submodule to any *-services/synoptic/techui-support. It is important this is done using `git submodule add ` otherwise the .gitmodules file is not created or updated causing the pod to be stuck in an error state.
2. Give an example of the tool via uvx showing that a devcontainer is required
3. Potentially not the right place to put it but there should be some documentation on setting up the *-synoptic service for the web gui