Add a Readme file for Bruzual and Charlot 2003 models

database_builder/bc03/README.rst

+The files in this directory were downloaded from http://www.bruzual.org on April
+2013.
+
+They are the Bruzual and Charlot (2003) low resolution Padova 1994 models with
+some *color* files containing useful informations for pcigale. On the original
+site, they can be found in the bc03.models.padova_1994_chabrier_imf.tar.gz and
+bc03.models.padova_1994_salpeter_imf.tar.gz archives.
+