DOC: Add single linkage
Add single linkage to a place in the docs where it was forgotten.
@@ -554,6 +554,8 @@ metric used for the merge strategy:
observations of pairs of clusters.
- **Average linkage** minimizes the average of the distances between all
observations of pairs of clusters.
+- **Single linkage** minimizes the distance between the closest
+ observations of pairs of clusters.
:class:`AgglomerativeClustering` can also scale to large number of samples
when it is used jointly with a connectivity matrix, but is computationally
