Fix definition for bulk write update operation (#1669)

Author: isabelatkinson

source/crud/bulk-write.md

@@ -518,10 +518,15 @@ If the document to be inserted does not contain an `_id` field, drivers MUST gen
     "multi": Optional<Boolean>,
     "upsert": Optional<Boolean>,
     "arrayFilters": Optional<Array>,
-    "hint": Optional<Document | String>
+    "hint": Optional<Document | String>,
+    "collation": Optional<Document>
 }
 ```
 
+The `update` command document is used for update and replace operations. For update operations, the `updateMods` field
+corresponds to the `update` field in `UpdateOneModel` and `UpdateManyModel`. For replace operations, the `updateMods`
+field corresponds to the `replacement` field in `ReplaceOneModel`.
+
 #### Delete
 
 ```javascript
@@ -866,6 +871,8 @@ batch-splitting to standardize implementations across drivers and simplify batch
 
 ## **Changelog**
 
+- 2024-09-25: Add `collation` field to `update` document and clarify usage of `updateMods`.
+
 - 2024-09-25: Update the `partialResult` population logic to account for ordered bulk writes.
 
 - 2024-09-18: Relax numeric type requirements for indexes.