Add missing copyright header to PermissionUtil

Signed-off-by: Álvaro Brey Vilas <alvaro.brey@nextcloud.com>

src/main/java/com/owncloud/android/utils/PermissionUtil.kt

@@ -1,3 +1,24 @@
+/*
+ * Nextcloud Android client application
+ *
+ * @author Álvaro Brey Vilas
+ * Copyright (C) 2021 Álvaro Brey Vilas
+ * Copyright (C) 2021 Nextcloud GmbH
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
 package com.owncloud.android.utils
 
 import android.Manifest