Index-time Boosts not supported by Lucene 7 and Solr 8 anymore

[hoesli]

The funtionality to boost at Index-time is removed form Lucene 7 and is now producing errors in Solr8. It was removed in conjunction with the improvements for nested document support.

Using boost insearchable block will generate an error in Solr. In Solr 7 it is still allowed (although it logs a warning in the logs)
The error in Solr 8 is Unknown operation for the an atomic update: value

This is because sunspot is sending the boost block similar to: {"id":"1", "val_s":{"value":"foo", "boost":2.0}}

See Indexing Changes in 8.0 > Index-time Boosts

If you want to use sunspot with Solr 8, use boost_fields in fulltext block at search time instead.

Could somebody update the readme?