chore: import upstream snapshot with attribution

code/_convenience_scripts/blank_tocs/ch11.toc

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+Grouping objects by similarity using k-means
+  K-means++
+  Hard versus soft clustering
+  Using the elbow method to find the optimal number of clusters
+  Quantifying the quality of clustering via silhouette plots
+Organizing clusters as a hierarchical tree
+  Performing hierarchical clustering on a distance matrix
+  Attaching dendrograms to a heat map
+  Applying agglomerative clustering via scikit-learn
+Locating regions of high density via DBSCAN
+Summary