Update mapping.md (#1374)

added one bullet to Explicit mapping to indicate the field can be
vectorized

Author: serenachou

manage-data/data-store/mapping.md

@@ -56,6 +56,7 @@ Use [explicit mapping](/manage-data/data-store/mapping/explicit-mapping.md) to d
 Defining your own mappings enables you to:
 
 * Define which string fields should be treated as full-text fields.
+* Define which text field can be automatically vectorized by a semantic search machine learning model. 
 * Define which fields contain numbers, dates, or geolocations.
 * Use data types that cannot be automatically detected (such as `geo_point` and `geo_shape`.)
 * Choose date value [formats](elasticsearch://reference/elasticsearch/mapping-reference/mapping-date-format.md), including custom date formats.
@@ -100,4 +101,4 @@ Defining too many fields in an index can lead to a mapping explosion, which can
 
 Consider a situation where every new document inserted introduces new fields, such as with [dynamic mapping](/manage-data/data-store/mapping/dynamic-mapping.md). Each new field is added to the index mapping, which can become a problem as the mapping grows.
 
-Use the [mapping limit settings](elasticsearch://reference/elasticsearch/index-settings/mapping-limit.md) to limit the number of field mappings (created manually or dynamically) and prevent documents from causing a mapping explosion.
+Use the [mapping limit settings](elasticsearch://reference/elasticsearch/index-settings/mapping-limit.md) to limit the number of field mappings (created manually or dynamically) and prevent documents from causing a mapping explosion.