We are considering automating this process and allowing access for Pearl users directly to the repos for an easier installation via composer but at this moment we are using private repos and theme install via composer is available only for internal use. The same applied for individual extensions.
However, there is a way to install the theme via composer until we automate this process.
You can create private repositories for all Pearl modules / theme (about 20 repos as the theme is modular). You'll need to add each module and theme to a separate repo in your organisation and proceed with the installation via composer using your own private repos. Once all repos are created you'll also be able to install the theme via composer.
What repos do I need to create?
Step 1: In the Theme Pack go to app/code/WeltPixel/ and check the folder structure.
Step 2: In Github or other versioning environment create one private repo for each theme module, following the name from readme of each module. Make sure the repo is private as using a public repo would mean sharing the code with the public and breaking the WeltPixel license agreement.
Example for 'Backend' extension:
create a private repo yourcompany/m2-weltpixel-backend.git and add the code from 'Backend' directory to this repo.
Do this for all the extensions under app/code/WeltPixel/
Step 3: Go to app/design/frontend/Pearl/ and create a repository for the theme 'weltpixel' and the sub-theme 'weltpixel_custom' following the Step 2 instructions.
I created my repos, how do I proceed with the composer installation?
Install Pearl Theme using composer instructions from readme file from Pearl Theme and each associated module, but keep in mind that you need to use the name of your organisation for each repo location.
Example of composer installation instructions, for 'Backend' extension:
composer config repositories.yourcompany-m2-weltpixel-backend git firstname.lastname@example.org:yourcompany/m2-weltpixel-backend.git
composer require yourcompany/m2-weltpixel-backend:dev-master
How to install only 1 extension via composer?
In this case you will only need 2 repos, one for 'Backend' shared pack and one for the extension that you need to install. The process of creating the repositories is the same as described in the steps above.