And for the record, this is what you'd like to insert into LocalSettings.php:
Code:
$wgGroupPermissions['*']['createaccount'] = false;
$wgGroupPermissions['*']['edit'] = false;
$wgGroupPermissions['user']['edit'] = false;
$wgGroupPermissions['sysop']['edit'] = true;
You could replace the last
true with
false if you want
absolutely nobody to edit pages.