Don't force the package type

phpstan/extension-installer will work if the package type is
`phpstan-extension` or if the `extra.phpstan.includes` key is
configured.

README.md

@@ -50,7 +50,7 @@ And that's it.
 
 ## Instructions for extension developers
 
-Extension's composer package [type](https://getcomposer.org/doc/04-schema.md#type) has to be set to `phpstan-extension` for this plugin to be able to recognize it.
+It's best (but optional) to set the extension's composer package [type](https://getcomposer.org/doc/04-schema.md#type) to `phpstan-extension` for this plugin to be able to recognize it and to be [discoverable on Packagist](https://packagist.org/explore/?type=phpstan-extension).
 
 Only one feature is supported right now: PHPStan is able to automatically include the extension's config files, without you having to mention them in your `phpstan.neon`'s `includes` section.
 

src/Plugin.php

@@ -82,7 +82,10 @@ public function process(Event $event): void
 
 		$data = [];
 		foreach ($composer->getRepositoryManager()->getLocalRepository()->getPackages() as $package) {
-			if ($package->getType() !== 'phpstan-extension') {
+			if (
+				$package->getType() !== 'phpstan-extension'
+				&& !isset($package->getExtra()['phpstan'])
+			) {
 				if (
 					strpos($package->getName(), 'phpstan') !== false
 					&& !in_array($package->getName(), [