(DOCS-13770): Clarifications to bucketAuto

Author: jeff-allen-mongo

source/reference/operator/aggregation/bucketAuto.txt

@@ -23,11 +23,20 @@ Definition
    documents into the specified number of buckets.
 
    Each bucket is represented as a document in the output. The document
-   for each bucket contains an ``_id`` field, whose value specifies the
-   inclusive lower bound and the exclusive upper bound for the bucket,
-   and a ``count`` field that contains the number of documents in the
-   bucket. The ``count`` field is included by default when the
-   ``output`` is not specified.
+   for each bucket contains:
+   
+   - An ``_id`` object that specifies the bounds of the bucket.
+   
+     - The ``_id.min`` field specifies the inclusive lower bound for the
+       bucket.
+
+     - The ``_id.max`` field specifies the upper bound for the bucket.
+       This bound is exclusive for all buckets except the final
+       bucket in the series, where it is inclusive.
+
+   - A ``count`` field that contains the number of documents in the
+     bucket. The ``count`` field is included by default when the
+     ``output`` document is not specified.
 
    The :pipeline:`$bucketAuto` stage has the following form: