README.md added in configurations folder

configurations/README.md

+Simulink configurations are stored
+in configurations_container.sldd 
+There is one configuration for
+simulation and a number of
+configurations for code generation.
+This is necessary as code generation
+config may vary depending on
+algorithm content (different tmf file,
+additional libs, includes, 
+custom code ecc.)
+
+There are functions to manually
+handle this container:
+
+- config_set_diags.m: a function
+for defining the diagnostic part
+for configSettings
+- config_update_diags.m: calls the
+previous and updates diags in
+the sldd 
+- config_export_to_base_and_scripts.m:
+exports the content of configurations
+sldd to base workspace and files
+
+