Add julia installation note, and link to caching section

Author: MichaelHatherly

docs/computations/julia.qmd

@@ -12,6 +12,13 @@ Quarto supports executable Julia code blocks within markdown. This allows you to
 
 Quarto has two available engines for executing Julia code. The older one is using the [IJulia](https://github.com/JuliaLang/IJulia.jl) Jupyter kernel and depends on Python to run. The newer engine is using the [QuartoNotebookRunner.jl](https://github.com/PumasAI/QuartoNotebookRunner.jl/) package to render notebooks and does not have any additional dependencies beyond a Julia installation.
 
+To use either of these engines will require that you manually install Julia if
+you have not done so already. You can download it from
+https://julialang.org/downloads/. There are two options for installation: the
+Juliaup installation manager, and the "manual" installation approach. Unless
+you know that you need to use the "manual" approach you should prefer using
+Juliaup since it allows you to manage multiple Julia versions on your system.
+
 ## Using the `jupyter` engine
 
 Below we'll describe how to [install](#installation) IJulia and related requirements but first we'll cover the basics of creating and rendering documents with Julia code blocks.

docs/projects/code-execution.qmd

@@ -68,7 +68,7 @@ This sub-directory render won't use the cached `freeze` results but instead will
 
 ## Cache
 
-You can use the `cache` option to cache the results of computations (using the [knitr cache](https://yihui.org/knitr/demo/cache/) for R documents, and [Jupyter Cache](https://jupyter-cache.readthedocs.io/en/latest/) for Jupyter documents):
+You can use the `cache` option to cache the results of computations (using the [knitr cache](https://yihui.org/knitr/demo/cache/) for R documents, [Jupyter Cache](https://jupyter-cache.readthedocs.io/en/latest/) for Jupyter documents, or [`engine: julia`'s](../computations/julia.qmd#caching-1) built-in support):
 
 ``` yaml
 execute: