Add script to run phpmd with composer

.phpmd-ruleset.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0"?>
-<ruleset name="My first PHPMD rule set"
+<ruleset name="Friendica Ruleset"
          xmlns="http://pmd.sf.net/ruleset/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://pmd.sf.net/ruleset/1.0.0

composer.json

@@ -160,6 +160,7 @@
 	"scripts": {
 		"test": "phpunit",
 		"test:unit": "phpunit -c tests/phpunit.xml --testsuite unit",
+		"phpmd": "phpmd src/ text .phpmd-ruleset.xml",
 		"phpstan": "phpstan analyze --memory-limit 1024M --configuration .phpstan.neon",
 		"lint": "find . -name \\*.php -not -path './vendor/*' -not -path './view/asset/*' -print0 | xargs -0 -n1 php -l",
 		"docker:translate": "docker run --rm -v $PWD:/data -w /data friendicaci/transifex bin/run_xgettext.sh",