Support for Composer installer paths

[davidgreenwald-sage]

Is your enhancement related to a problem? Please describe.

When installing from Packagist, Composer will place this plugin in the vendor folder if the dependency composer/installers is not present in the user/developer's local composer.json, which is required to enable custom path support such as loading this to a plugins directory with installer-paths or for the expected default of wp-content/plugins. This requirement should be present here in the repo's composer.json per Composer's documentation

Describe the solution you'd like

Add "composer/installers": "~1.0", to the requires section of composer.json.