Make the devdocs more complete and self-contained (#252)

* Make the devdocs more complete and self-contained

* Rename devdocs/misc-notes-from-contributors.md to devdocs/misc/misc_notes_for_committers.md

* Document the dependencies of the build script

* No need to manually make multiple commits

---------

Co-authored-by: Ian Butterworth <i.r.butterworth@gmail.com>

devdocs/local_setup.md

@@ -0,0 +1,47 @@
+# Local development
+
+## 1. Clone the repo
+
+```bash
+git clone git@github.com:julia-actions/setup-julia.git
+cd setup-julia
+```
+
+## 2. Install NodeJS
+
+### Unix, using `asdf` (recommended, but not required)
+
+First, make sure that you have installed [`asdf`](https://asdf-vm.com/) on your local machine.
+
+Then, `cd` to your clone of the repo and run the following commands:
+
+```bash
+asdf plugin add nodejs
+asdf install
+```
+
+This will use `asdf` to install the correct version of NodeJS.
+
+### Unix, but not using `asdf`
+
+Instead of using `asdf`, you can instead choose to install NodeJS manually.
+
+First, check the `.tool-versions` file in this repo, and see what version of NodeJS you need. Then, install that same version of NodejS on your local machine.
+
+### Windows
+
+`asdf` does not (currently) support Windows. So on Windows, you have to install NodeJS manually.
+
+First, check the `.tool-versions` file in this repo, and see what version of NodeJS you need. Then, install that same version of NodejS on your local machine.
+
+## 3. Working locally
+
+First, `cd` to your clone of the repo. Now you can run the following commands:
+
+```bash
+npm ci
+
+npm run build
+```
+
+When you are ready, you can commit your changes and push them to your PR.