Documenting String.raw (#1198)

* Documenting String.raw

* Typo

* Rewrite String.raw doc

README.md

@@ -30,6 +30,13 @@ Call `katex.render` with a TeX expression and a DOM element to render into:
 katex.render("c = \\pm\\sqrt{a^2 + b^2}", element);
 ```
 
+To avoid escaping the backslash (double backslash), you can use
+[`String.raw`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/raw)
+(but beware that `${`, `\u` and `\x` may still need escaping):
+```js
+katex.render(String.raw`c = \pm\sqrt{a^2 + b^2}`, element);
+```
+
 If KaTeX can't parse the expression, it throws a `katex.ParseError` error.
 
 #### Server side rendering or rendering to a string