add _default clarification in docs

Author: collerek

docs/queries/create.md

@@ -63,6 +63,9 @@ Combination of create and get methods.
 Tries to get a row meeting the criteria and if `NoMatch` exception is raised it creates
 a new one with given kwargs and _defaults.
 
+When `_defaults` dictionary is provided the values set in `_defaults` will **always** be set, including overwriting explicitly provided values. 
+i.e. `get_or_create(_defaults: {"title": "I win"}, title="never used")` will always use "I win" as title whether you provide your own value in kwargs or not. 
+
 ```python
 class Album(ormar.Model):
     class Meta:
@@ -187,4 +190,4 @@ from other side of the relation.
 [models-save]: ../models/methods.md#save
 [models-upsert]: ../models/methods.md#upsert
 [models-save-related]: ../models/methods.md#save_related
-[querysetproxy]: ../relations/queryset-proxy.md
+[querysetproxy]: ../relations/queryset-proxy.md