add infos about OSVVM library

README.md

@@ -59,7 +59,8 @@ Unit tests for SpiSlave component
 ## Dependencies
 To run the tests, you have to install GHDL. You can get it from
 [http://sourceforge.net/projects/ghdl-updates/](http://sourceforge.net/projects/ghdl-updates/).
-Furthermore, you need the VHDL 2008 proposed packages because I'm using various VHDL 2008 features.
+
+Furthermore, you need the VHDL 2008 proposed packages because libvhdl uses various VHDL 2008 features.
 You can get the packages from [http://www.eda.org/fphdl/](http://www.eda.org/fphdl/).
 Save the following files into the test folder:
 
@@ -70,6 +71,14 @@ Save the following files into the test folder:
 * numeric_std_unsigned_c.vhd
 * env_c.vhd
 
+If you another simulator with full VHDL-08 support, you don't need these packages. Instead you have to outcomment
+the references to these packages from the source files.
+
+libvhdl also uses the OSVVM library to generate random data for the unit tests. We use version OSVVM version 2.1
+because of restrictions of the current GHDL release. You can find it under the osvvm_2.1 folder in the test/
+directory. If you use another simulator with full OSVVM support, you can download newer versions of the library
+from [http://osvvm.org](http://osvvm.org).
+
 Another useful tool is GTKWave, install it if you want to use the waveform files generated by some of the tests.