docs: add random=true to lipsum shortcode

Fixes quarto-dev/quarto-cli#11664

Author: mcanouil

docs/authoring/lipsum.qmd

@@ -30,3 +30,9 @@ Here's an example of `lipsum` generating two paragraphs of text, by adding `{{{<
 
 - `{{{< lipsum nparas >}}}`: `nparas` describes the number of paragraphs of placeholder text to include in the document. 
 - `{{{< lipsum start-end >}}}`: `start` and `end` are two numbers that describe the range of lorem ipsum paragraphs to include in the document.
+
+`lipsum` generates the placeholder text in a deterministic way[^1], so the same parameters will always generate the same text, but using `random=true` will generate a paragraph or random set of paragraphs.
+
+- `{{{< lipsum 1 random=true >}}}`: This will generate a single paragraph of random lorem ipsum text.
+
+[^1]: Since 1.7.14. Earlier versions of Quarto generates random text.