doc: update installation instructions due to pkg deprecation

[askingcat]

pkg has been recently deprecated:

[!IMPORTANT]
pkg has been deprecated with 5.8.1 as the last release. There are a number of successful forked versions of pkg already with various feature additions. Further, we’re excited about Node.js 21’s support for single executable applications. Thank you for the support and contributions over the years. The repository will remain open and archived.

The README currently instructs the user to use it, however, so a replacement should be found:

git clone https://github.com/bitnami/readme-generator-for-helm
cd ./readme-generator-for-helm
npm install
npm install -g pkg
pkg . -o readme-generator-for-helm

I'm unfortunately not that familiar with the JavaScript ecosystem, so can't directly recommend you e.g. a specific fork myself.

[davidmdm]

I wanted a way to install this on my system. pkg wasn't working, the npm install instructions wasn't working.

I ended up simply using esbuild to bundle the entire application, and copied the resulting file to my path. I think this solution can be considered.

[fmulero]

Related to #95