This is a default page provided when you install QGIS Web Client. The default installation assumes that you checkout the QGIS Web Client from github into the directory "/home/web/qgis-web-client". To start with the client configuration, please copy one of the "site/js/GlobalOptions.js.templ" template files into "site/js/GlobalOptions.js". If you use different paths, please adjust them accordingly on this landing page (site/index.html) and in the file "site/js/GlobalOptions.js". You will also have to install QGIS Server (FCGI) and Apache with the FCGID module. You will have to configure Apache for FCGI use any your document locations.