Document searchable snapshots supported repos (#69508)
Document searchable snapshots supported repos (#69508)

Adds a note listing the repository types that can be used with
searchable snapshots.
robin13/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch