Document that the unified highlighter supports matched_field

This highlighter should now support matched_field add a quick mention
about it.

Signed-off-by: David Causse <[email protected]>

Author: nomoa

_search-plugins/searching-data/highlight.md

@@ -206,7 +206,7 @@ fragment_offset | Specifies the character offset from which you want to start hi
 number_of_fragments| The maximum number of returned fragments. If `number_of_fragments` is set to 0, OpenSearch returns the highlighted contents of the entire field. Default is 5.
 `order` | The sort order for the highlighted fragments. Set `order` to `score` to sort fragments by relevance. Each highlighter uses a different algorithm to calculate relevance scores. Default is `none`.
 `highlight_query` | Specifies that matches for a query other than the search query should be highlighted. The `highlight_query` option is useful when using a faster query to get document matches and a slower query (for example, `rescore_query`) to refine the results. We recommend including the search query as part of the `highlight_query`.
-`matched_fields` | Combines matches from different fields to highlight one field. The most common use case for this functionality is highlighting text that is analyzed in different ways and kept in multi-fields. All fields in the `matched_fields` list must have the `term_vector` field set to `with_positions_offsets`. The field in which the matches are combined is the only loaded field, so it is beneficial to set its `store` option to `yes`.  Valid only for the `fvh` highlighter.
+`matched_fields` | Combines matches from different fields to highlight one field. The most common use case for this functionality is highlighting text that is analyzed in different ways and kept in multi-fields. If using `fvh`, all fields in the `matched_fields` list must have the `term_vector` field set to `with_positions_offsets`. The field in which the matches are combined is the only loaded field, so it is beneficial to set its `store` option to `yes`. Valid only for the `fvh` and `unified` highlighters.
 `no_match_size` | Specifies the number of characters, starting from the beginning of the field, to return if there are no matching fragments to highlight. Default is 0.
 `phrase_limit` | The number of matching phrases in a document that are considered. Limits the number of phrases to be analyzed by the `fvh` highlighter in order to avoid consuming a lot of memory. If `matched_fields` are used, `phrase_limit` specifies the number of phrases for each matched field. A higher `phrase_limit` leads to increased query time and more memory consumption. Valid only for the `fvh` highlighter. Default is 256.
 `max_analyzer_offset` | Specifies the maximum number of characters to be analyzed by a highlight request. The remaining text will not be processed. If the text to be highlighted exceeds this offset, then an empty highlight is returned. The maximum number of characters that will be analyzed for a highlight request is defined by `index.highlight.max_analyzed_offset`. When this limit is reached, an error is returned. Set the `max_analyzer_offset` to a lower value than `index.highlight.max_analyzed_offset` to avoid the error.