Corrected an incomplete sentence. (elastic#86542)

* Corrected an incomplete sentence.

* Update docs/reference/aggregations/metrics/avg-aggregation.asciidoc

Co-authored-by: Christos Soulios <[email protected]>

Co-authored-by: David Kilfoyle <[email protected]>
Co-authored-by: Christos Soulios <[email protected]>

Author: 3 people

docs/reference/aggregations/metrics/avg-aggregation.asciidoc

@@ -4,7 +4,7 @@
 <titleabbrev>Avg</titleabbrev>
 ++++
 
-A `single-value` metrics aggregation that computes the average of numeric values that are extracted from the aggregated documents. These values can be extracted either from specific numeric fields in the documents.
+A `single-value` metrics aggregation that computes the average of numeric values that are extracted from the aggregated documents. These values can be extracted either from specific numeric or <<histogram,histogram>> fields in the documents.
 
 Assuming the data consists of documents representing exams grades (between 0
 and 100) of students we can average their scores with: