Hello, I've installed flarum via apache from this guide. After completing the installation I can not access the flarum setup wizard. My site just shows the installation folder structure:

Apache's error log says the error is:
AH01276: Cannot serve directory /var/www/html/flarum/: No matching DirectoryIndex (index.html,index.cgi,index.pl,index.php,index.xhtml,index.htm) found, and server-generated directory index forbidden by Options directive
Does anyone here know how I can fix this?