Add a basic child theme template

[ryelle]

This is a basic child theme template, which will use the wporg-parent-2021 theme as its parent. It also includes a script to generate the project, using the same mustache template engine as create-block, so our templates are the same between #21 & here.

The create script I've written here is PHP - I did that rather than creating a new package.json so I could use JS. It's very simple, inspired from create-block. I had thought maybe we could switch out different templates depending on the argument -- so this has create child-theme, but we could also do create env to create a full env with .wp-env.json, etc.

$ ./bin/create child-theme

Let's create a child theme project!
Hit enter to accept the default values.

The display title for the theme [default: Child Theme]: 
The theme slug used for identification (also the output folder name) [default: wporg-child-theme]: 
The short description for the theme: 
The textdomain used for this theme [default: wporg]: 

Generating theme…

Tada! Theme created in /full/path/to/wporg-child-theme

This wouldn't generate blocks — the block template in #21 can be used with @wordpress/create-block to create mu-plugins blocks, and any blocks we want to create as standalone plugins can just be vanilla @wordpress/create-block (or we can make another template).

[ryelle]

Switching this out of draft mode, though I'm still looking for feedback on the idea as well as the code.