Add an option for blueprint.json overrides and extensions

[karimStekelenburg]

First of all, thanks for the efforts on this. I think this is an amazing idea! 🙏

What I think could be a very valuable addition, is the option to override certain variables in the blueprint.json, as well as extend it.

Scenario:

I work for a company and would like to use this project as a way to standardize our READMEs. There are a lot of components of the READMEs that are the same across all repositories. For example: our logo and company website will be the same, regardless of the project. Because of this, my thought was to create a separate repository, where I would store a base-blueprint.json, containing all the 'generic' elements of the READMEs we would create.

However, there are also quite some project specific elements as well, where some of which may conflict with the elements specified in the base-blueprint.md. For example: if we collaborate with another company on this specific project, the logo we want to show might be a combination of our logo, as well as the logo of the other company.

I think it would be very useful to have the option to extend the blueprint.json file with an additional 'project specific' file.

For example:

Combining base-blueprint.json with project-blueprint.json would merge the two files together, resulting in a JSON object that merged all unique keys of both files together, allowing for extension. Also, if the same key exists in both base-blueprint.json and project-blueprint.json, it would take the value of project-blueprint.json, allowing for overrides.