Add a deprecation notice to the readme
Add a deprecation notice to the readme

Add a deprecation notice as part of the process of deprecating the gem and moving it to the [samvera-deprecated](https://github.com/samvera-deprecated) organization.

See https://github.com/samvera/maintenance/issues/19
And https://samvera.github.io/deprecation.html
projecthydra/solrizer