Update README.md a bit.

README.md

-# BiscuIT-ng
+# BiscuIT School Information System (SIS) - Next Generation Platform
 
-BiscuIT School Information System (SIS) - Next Generation Platform
\ No newline at end of file
+## What BiscuIT is
+
+BiscuIT is a web-based school information system (SIS) which can be used to
+manage and/or publish organisational subjects of educational institutions.
+
+It was originally developed together with Städt. Leibniz-Gymnasium Remscheid
+as a proprietary product. Five years after the school stole the original
+code base, BiscuIT-ng started as a complete re-implementation as
+well-designed, free and open source software.