chore: Add bloom filter related comments (#726)

* chore: Add bloom filter related comments

PiperOrigin-RevId: 538646627

Source-Link: googleapis/googleapis@1ceef69

Source-Link: googleapis/googleapis-gen@fb7c4c4
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packages/google-cloud-firestore/google/cloud/firestore_v1/types/write.py

@@ -472,6 +472,9 @@ class ExistenceFilter(proto.Message):
             If different from the count of documents in the client that
             match, the client must manually determine which documents no
             longer match the target.
+
+            The client can use the ``unchanged_names`` bloom filter to
+            assist with this determination.
         unchanged_names (google.cloud.firestore_v1.types.BloomFilter):
             A bloom filter that contains the UTF-8 byte encodings of the
             resource names of the documents that match