* Update information on required compiler version

        For issue #47

doc/installation.rst

@@ -31,6 +31,8 @@ An Ada compiler:
    versions installed. See below explanations on the ADA environment
    variable if you need to override the default guess.
 
+.. note:: Ocarina requires at least GCC/FSF 5.1 or GNAT GPL 2015 to be compiled.
+
 Optional components:
 
 * GNATColl for the Ocarina Python bindings