docs: add note about masternode identities to getIdentityByPublicKeyHash (#86)

* docs: add note about masternode identities to getIdentityByPublicKeyHash

* style: wrap

Author: thephez

docs/reference/dapi-endpoints-platform-endpoints.md

@@ -725,6 +725,11 @@ grpcurl -proto protos/platform/v0/platform.proto \
 
 **Returns**: An [identity](../explanations/identity.md) associated with the provided public key hash
 
+:::{note}
+This endpoint only works for unique keys. Since masternode keys do not have to be unique (e.g.,
+voting keys), some masternode identities cannot be retrieved using this endpoint.
+:::
+
 **Parameters**:
 
 | Name    | Type    | Required | Description |