[Discover][docs] Add search for relevance

docs/discover/search-for-relevance.asciidoc

@@ -0,0 +1,24 @@
+[[discover-search-for-relevance]]
+== Search for relevance
+Sometimes you might be unsure which documents best match your question. 
+{es} assigns a relevancy, or score to each document, so you can
+can narrow your search to the documents with the most relevant results.
+The higher the score, the better it matches your query.
+
+For example, suppose you have the <<gs-get-data-into-kibana, sample flights data set>>, and you're a searching for
+a flight that arrived or departed from `Warsaw` or `Venice` when the weather was clear.
+
+.  In *Discover*, open the index pattern dropdown, and select `kibana_sample_data_flight`.
+.  In the query bar, click  *KQL*, and switch to the <<lucene-query, Lucene query syntax>>.
+. Search for `Warsaw OR Venice OR Clear`.
+.  If you don't see any results, open the time filter and select a time range that contains data.
+.  From the list of *Available fields*, add `_score` to the document table.
+. In the document table, click the header for the `_score` column, and then sort the column by descending scores.
++
+The results are currently sorted by first `Time`, and then by `_score`.
+. To sort only by `_score`, remove the `Time` field.
++
+Your table now shows documents with the best matches, from most to least relevant.
++
+[role="screenshot"]
+image::images/discover-search-for-relevance.png["Example of a search for relevance"]

docs/user/discover.asciidoc

@@ -198,7 +198,6 @@ image:images/visualize-from-discover.png[Visualization that opens from Discover
 [float]
 === What’s next?
 
-
 * <<kuery-query, Learn more about the structure of a KQL query>>.
 
 * <<kibana-discover-settings, Configure Discover>> to better meet your needs.
@@ -209,10 +208,14 @@ the table columns that display by default, and more.
 
 * <<reporting-getting-started, Present your findings in a report>>.
 
+* <<discover-search-for-relevance, Search for relevance>>.
+
 --
 
 include::{kib-repo-dir}/management/index-patterns.asciidoc[]
 
 include::{kib-repo-dir}/discover/set-time-filter.asciidoc[]
 
 include::{kib-repo-dir}/discover/search.asciidoc[]
+
+include::{kib-repo-dir}/discover/search-for-relevance.asciidoc[]