updating neighbor joining documentation

src/neighbor-join.js

@@ -82,6 +82,23 @@ function getTotalDistances(distanceMatrix) {
  return _.map(distanceMatrix, _.sum);
 }
 
+/**
+ * Create a neighbor joining tree from a distance matrix
+ * See test/neighbor-join-test.js for a working example
+ *
+ * @param {Array} distanceMatrixArr The NxN distance matrix.
+ * const D = [
+ * [0, 5, 9, 9, 8],
+ * [5, 0, 10, 10, 9],
+ * [9, 10, 0, 8, 7],
+ * [9, 10, 8, 0, 3],
+ * [8, 9, 7, 3, 0]
+ * ];
+ * 
+ * @param {Number} n The dimension of the distanceMatrixArr.
+ * @param {Array} nodeList The names of each row in the distanceMatrix
+ * @returns The neighbor joining new tree.
+ */
 export default function neighborJoining(distanceMatrixArr, n, nodeList) {
  if (n <= 2) {
  let tree = new phylotree("");