Add formulas and more context for some matrix algorithms

[krivonogov]

• anomaly reference to the exact formula
• similarity reference to the exact formula
• truncate update docstring with all use-cases
• tail_clustering reference to exact algorithm
• affinity_clusters reference to exact algorithm
• co_clustering reference to exact algorithm and method's doc
• nmf reference to exact algorithm and parameters description
• nmf_approximation parameters description
• nmf_fold reference to exact algorithm