1. Rename this to: installed_app_ids.txt
2. Add all apps IDs (each on a separate line) that should be reported as insatlled, they could be NOT owned, that is allowed
3. Or, remove the file installed_app_ids.txt if it exists to:
    * Allow app ID 0, this seems to be a special denotation to "non-steam apps"
    * Allow app ID of the current game (you must create the file steam_appid.txt)
    * Allow anything else

In all cases app ID 4294967295 is disallowed