improved description

README.md

@@ -5,7 +5,7 @@ Politecnico di Milano
 University of Milan
 
 Material:
-- _py-scripts_ includes Python (3.6 or later) scripts; most of them require the [btclib](https://github.com/dginst/btclib) library;
-- _excel_: includes Excel spreadsheets with elliptic curve examples;
-- _regtest-lab_: includes information for a regtest session using Bitcoin Core;
-- the latest version of the slides is available from the latest course page at <http://www.ametrano.net/bbt/>.
+- the _py-scripts_ folder includes Python (3.6 or later) scripts: most of them require the [btclib](https://github.com/dginst/btclib) library;
+- the _excel_ folder includes Excel spreadsheets illustrating finite fields and elliptic curves;
+- the _regtest-lab_ folder includes information for a regtest session using Bitcoin Core;
+- the latest version of the course slides is available from the course page at <http://www.ametrano.net/bbt/>.