When trying to install MediaWiki without having ran composer, the user gets the following error:
```
MediaWiki requires the PSR-3 logging library to be present. This library is not embedded directly in MediaWiki's git repository and must be installed separately by the end user. Please see mediawiki.org for help on installing the required components.
Fatal error: MediaWiki requires the PSR-3 logging library to be present. This library is not embedded directly in MediaWiki's git repository and must be installed separately by the end user. Please see mediawiki.org for help on installing the required components. in /Users/ori/www/w/includes/debug/logger/Factory.php on line 101
```
* It assumes the user is installing via Git.
* The error message is repeated.
* The look and feel of the error message is not consistent with the web installer.
The web installer should check for composer dependencies using the same UI it uses to make other checks for the suitability of the environment for running MediaWiki.