The `php` command cannot be found. Please verify that PHP is installed, or set the `php.executables` setting.
Open Settings.json and put this codes below: for wamp users
"php.validate.executablePath": "C:\wamp64\bin\php\php7.1.9\php.exe",
"php.executablePath": "C:\wamp64\bin\php\php7.1.9\php.exe"