docs: sovereign adapter

[pepyakin]

https://github.com/thrumdev/blobs/tree/main/adapters/sovereign

Update README.md for the sovereign adapter. Right now it is just the template copy pasta. The readme should try better at being useful. It may describe the architecture and maybe link to the copy of the template, but I think it would be better if it talked about things like how to integrate it into a project, anything that a developer looking to integrate it with a sov based rollup should know.