Apply suggestions from code review

Co-authored-by: Marko Bekhta <[email protected]>

Author: fax4ever

documentation/src/main/asciidoc/public/reference/_search-dsl-aggregation.adoc

@@ -347,7 +347,7 @@ The fields that are targeted by the aggregation function must be declared <<mapp
 
 The `sum` aggregation sums up the field values.
 
-.Sum the prices all of the science fiction books
+.Sum the prices of all science fiction books
 ====
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@@ -358,9 +358,10 @@ include::{sourcedir}/org/hibernate/search/documentation/search/aggregation/Aggre
 
 [NOTE]
 ====
-You can always use the field type for the expected returned type.
-Another option is to set `Double.class` for the expected returned type and you can always do it
-even if the field is not double typed.
+You can always use the field type for the expected returned value.
+Alternatively, as aggregations usually involve some mathematical computations,
+it is possible to request a `Double.class`  result, which will return the aggregated value
+as the corresponding search backend computed it.
 ====
 
 === Min metric aggregation
@@ -391,9 +392,9 @@ include::{sourcedir}/org/hibernate/search/documentation/search/aggregation/Aggre
 
 === Count metric aggregation
 
-The `count` aggregation counts the field values.
+The `count` aggregation counts the number of documents in which the field is not empty. 
 
-.Count anytime the price field has a value among all the science fiction books
+.Count the number of the science fiction books with prices
 ====
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@@ -404,7 +405,7 @@ include::{sourcedir}/org/hibernate/search/documentation/search/aggregation/Aggre
 
 === Count distinct metric aggregation
 
-The `count distinct` aggregation counts the different field values.
+The `count distinct` aggregation counts the number of unique field values.
 
 .Count anytime the price field has a different value among all the science fiction books
 ====
@@ -417,9 +418,9 @@ include::{sourcedir}/org/hibernate/search/documentation/search/aggregation/Aggre
 
 === Avg metric aggregation
 
-Applies the SQL `avg` aggregation function on a given numeric or temporal field.
+The `avg` aggregation calculates the average value of a given numeric or temporal field among the selected documents.
 
-.Compute the average of the prices all of the science fiction books
+.Compute the average price of all science fiction books
 ====
 [source, JAVA, indent=0, subs="+callouts"]
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