Describe what the library offers in README

Author: homeworkprod

README.md

@@ -1,5 +1,17 @@
 # Python library for the OrgaTalk LAN Party Database
 
+This library provides
+
+- party and party series models,
+- functionality to deserialize parties and party series from TOML, and
+- functionality to serialize parties (but not party series) to TOML
+
+to work with data for and from the public [LAN party database by
+OrgaTalk](https://lanpartydb.orgatalk.de/).
+
+Data and code repositories for the project are available at:
+https://github.com/lanpartydb
+
 
 ## Installation