If you can read this, you've (probably) installed Bolt in the wrong folder.
It's recommended to install Bolt outside the so-called web root, because this is generally seen as 'best practice', and it is good for overall security. The reason you are seeing this page, is that your web server is currently serving the incorrect folder as 'web root'. Or, to put it the other way around: This file should not be visible.
The current folder is:
The best and easiest fix is to configure the server to use
this 'document root':
Alternatively, move everything 'up' one level. So instead of extracting
.tgz file in this folder, extract