WP-NOW: Add examples using rewrite-wp-config and WP_DEBUG on Readme.

[sejas]

What?

Update the WP_DEBUG example to use the method rewrite-wp-config which avoids conflicting with other constants but it modifies the wp-config.php file shared across projects.

Why?

The current example works, but it displays warning in the Frontend:

Testing Instructions

• Read the readme https://github.com/WordPress/playground-tools/blob/update/wp-now-readme-rewrite-wp-config/packages/wp-now/README.md#using-blueprints