[FLINK-5597] [docs] Improve the LocalClusteringCoefficient documentation

[greghogan]

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[uce]

Changes read well. +1 to merge.

Small note on JavaDocs and usage of <br> tags: I think the common way is to use <p> when the paragraph starts.

/**
 * Hyperlink-Induced Topic Search computes two interdependent scores for every
 * vertex in a directed graph. A good "hub" links to good "authorities" and
 * good "authorities" are linked from good "hubs".
 * 
 * <p>This algorithm can be configured to terminate either by a limit on the number
 * of iterations, a convergence threshold, or both.
 * 
 * <p>http://www.cs.cornell.edu/home/kleinber/auth.pdf
 *
 * @param <K> graph ID type
 * @param <VV> vertex value type
 * @param <EV> edge value type
 */
public class HITS<K, VV, EV> {}

Of course, we don't have a code style ;-). Just wanted to mention it, I don't think that this needs changes with this PR.