add REACT_APP_NAME to env sample

[ethanppl]

Some users log path in client\src\components\Settings\AppForm.tsx, becomes ~/.config/undefined/logs/main.log.

Code in client\src\components\Settings\AppForm.tsx:

    const appName = process.env.REACT_APP_NAME;
    const platform = (window as any).platform;

    const linuxPath = `~/.config/${appName}/logs/main.log`;
    const macOSPath = `~/Library/Logs/${appName}/main.log`;
    const windowsPath = `%USERPROFILE%\\AppData\\Roaming\${appName}\\logs\\main.log`;