Clarify head-loading behaviour

README.md

@@ -41,8 +41,10 @@ sentence-transformers load **silently ignores it** and gives you the un-headed b
 | `pylate.models.ColBERT(...)` — plain load | base only, head ignored, **no error** | 19.61 |
 | `WeightedColBERT.from_base(...)` — see below | full model | **21.41** |
 
-There is no warning when the head is skipped. If you are reproducing the paper number,
-use the second path.
+There is no warning when the head is skipped, so if you are reproducing the paper
+number, use the second path. `WeightedColBERT.from_base` resolves the head from this
+repo automatically and **raises** if it cannot find one, so that path cannot fail
+silently. Pass `require_head=False` if you deliberately want the base.
 
 ---