Cannot add a file with Search API Attachments I'm using Search API with Solr and Tika under D8 to build a search engine on my website. 

I could not find any tutorial under D8 for that, so I followed one I've found on D7. However, when I try to add a field "file" to my index, it appears in a section called "Skipped fields" with the following message : 


  The following fields cannot be indexed since there is no type mapping
  for them:
  
  Source » File (type "entity:file")
  
  If you think one of these fields should be available for indexing,
  please report this in the module's issue queue. (Make sure to first
  search for an existing issue for this field.) Please note that
  entity-valued fields generally can be indexed by either indexing their
  parent reference field, or their child entity ID field.


Has anyone managed to index files using Search API Attachments ? I cannot understand how to fix this message. 

Also, it does not make sense to me to "index their parent reference field" because this will put an ID in Solr, and not a real text file metadata ..
there are some steps to follow in the module README.txt file :

https://cgit.drupalcode.org/search_api_attachments/tree/README.txt?h=8.x-1.x#n81