Just run an alter query on the table. I'm not sure what data type it has to be, but it'll look like something like ALTER TABLE items_base ADD COLUMN clothing_on_walk INT DEFAULT 0;
You've set it up incorrectly. It's trying to find your vendor folder in the public directory. I'd recommend cloning the repo into a parent folder in your htdocs and set it up from there.
Make sure you have Composer and Node installed on your computer. Clone the Goldfish repo into your htdocs folder and run composer install and npm install in the Goldfish folder. Fill out the .env file with your information. If there is no .env file, you can copy and rename the .env.example file...