Added link to PIC doc from the main clustering md doc

Author: sboeschhuawei

docs/mllib-pic-clustering.md renamed to docs/mllib-clustering-pic.md

@@ -34,6 +34,9 @@ a given dataset, the algorithm returns the best clustering result).
 * *initializationSteps* determines the number of steps in the k-means\|\| algorithm.
 * *epsilon* determines the distance threshold within which we consider k-means to have converged. 
 
+[Power Iteration Clustering]{'mllib-clustering-pic.md'} that uses the Power Iteration method combined with KMeans clustering to 
+cluster points based on a Gaussian measure of the input data pairwise similarity.
+
 ### Examples
 
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