Merge pull request #660 from THeK3nger/doc-mathjax-note

Add a note in MathJax documentation

Author: azerupi

book-example/src/format/mathjax.md

@@ -9,9 +9,13 @@ To enable MathJax, you need to add the `mathjax-support` key to your `book.toml`
 mathjax-support = true
 ```
 
->**Note:**  
+>**Note:**
 The usual delimiters MathJax uses are not yet supported. You can't currently use `$$ ... $$` as delimiters and the `\[ ... \]` delimiters need an extra backslash to work. Hopefully this limitation will be lifted soon.
 
+>**Note:**
+> When you use double backslashes in MathJax blocks (for example in commands such as `\begin{cases} \frac 1 2 \\ \frac 3 4 \end{cases}`) you need to add _two extra_ backslashes (e.g., `\begin{cases} \frac 1 2 \\\\ \frac 3 4 \end{cases}`).
+
+
 ### Inline equations
 Inline equations are delimited by `\\(` and `\\)`. So for example, to render the following inline equation \\( \int x dx = \frac{x^2}{2} + C \\) you would write the following:
 ```