[DOCS] Clearer instructions on functional parity between arborist and NPM

Hey there, as a preface, I appreciate everything you guys do to maintain npm and all of its workspaces.

I am trying to programmatically install modules into a project without using exec calls or the deprecated npm programmatic interface. Arborist is the perfect package for this endeavor. However, I am finding it difficult to understand how exactly I can use arborist to mimic an npm install exactly? Do I have to do more than this?

const arb = new Arborist(optionsObject)
await arb.loadActual()
await arb.loadVirtual()
await arb.buildIdealTree({})
await arb.reify();

That example omits error handling.

I guess I am more so confused on how the virtual and actual trees change with changes to a package.json file, and how Arborist handles that.

Thanks in advance.

Start with the Arborist call sequence shown in the issue and review how it is intended to correspond to npm install. Document how actual and virtual trees respond to package.json changes, whether additional steps are needed for functional parity, and how errors should be handled; the work is done when these questions are answered clearly for programmatic users.