Add a prerequisite for the Go compiler for go-jsonnet

The `gojsonnet` Python package requires a working Go compiler, since
no wheels are published for that package. This commit updates the PyPI
install instructions for Commodore with a prerequisite for a working Go
compiler.

docs/modules/ROOT/pages/explanation/running-commodore.adoc

@@ -22,6 +22,8 @@ We recommend that you install Python and the `venv` module with your preferred p
 * Additionally, a few of the Commodore Python package dependencies require a working C compiler, the Python 3 development package, and the FFI development package.
 On Linux distributions you'll want packages `python3-dev` or `python3-devel` and `libffi-dev` or `libffi-devel` respectively.
 Please refer to your operating system's documentation for instructions to setup a working C compiler.
+* Installing the `gojsonnet` Python package requires a working Go compiler.
+Please check your operating system's documentation for instructions to setup a working Go compiler.
 * On some Linux distributions, you may need to install the Python `wheel` package manually.
 * jsonnet-bundler from https://github.com/projectsyn/jsonnet-bundler/releases[projectsyn/jsonnet-bundler/releases] in your `$PATH` as `jb`.
 * Helm 3, https://helm.sh/docs/intro/install/[installation instructions]