docs: add dtype section

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---

Author: kgryte

lib/node_modules/@stdlib/ndarray/README.md

@@ -177,7 +177,7 @@ The namespace exports the following functions to inspect multidimensional arrays
 
 The namespace exports the following functions to index multidimensional arrays:
 
-<!-- <toc pattern="+(at|ind2sub|index|sub2ind)"> -->
+<!-- <toc pattern="+(at|ind2sub|index|index-modes|sub2ind)"> -->
 
 <div class="namespace-toc">
 
@@ -198,6 +198,14 @@ The namespace exports the following functions to convert multidimensional arrays
 
 <!-- </toc> -->
 
+##### Data Types
+
+The namespace exports the following functions for working with multidimensional array data types:
+
+<!-- <toc pattern="+(casting-modes|dtype-ctor|dtypes|input-casting-policies|min-dtype|mostly-safe-casts|next-dtype|output-dtype-policies|promotion-rules|safe-casts|same-kind-casts)"> -->
+
+<!-- </toc> -->
+
 ##### Sub-namespaces
 
 The namespace contains the following sub-namespaces: