Add "ingredient" for Mathjax to Cookbook

docs/user-documentation/extending.md

@@ -81,6 +81,14 @@ This repository is also a Drupal Feature that, when enabled as a module, will cr
 
 Command-line tool for ingesting (and updating) nodes and media from anywhere - you don't need to access to the Drupal server's command line. Provides robust data validation, flexible organization of your input data (can use CSV, Google Sheets, or Excel files) plus creation of taxonomy terms on the fly.
 
+### Richer Content
+
+#### Displaying equations and formulae
+
+[MathJax](https://www.drupal.org/project/mathjax)
+
+This module is a plug-and-play solution for rendering [LaTeX](https://www.latex-project.org/). It uses a CDN so no library has to be installed on your system, and the processing is done in the user's browser. In terms of Drupal, it provides a text filter that must be enabled in at least one text format (such as Full HTML). With this you can enter mathematical formulae in abstracts! Need to recognize unfamiliar symbols? Try this [LaTeX symbol reference](https://oeis.org/wiki/List_of_LaTeX_mathematical_symbols) thanks to the On-Line Encyclopedia of Integer Sequences.
+
 ### Search
 
 #### Custom search weighting