Add note about compatibility between F77 Compiler an blas.

README

@@ -108,11 +108,18 @@ BLAS -- "Basic Linear Algebra Subprograms"
 	and Opteron CPUs you should have a look at AMD's web-site
 	(www.amd.com) and search for "acml".
 
-	Known quirks for specific BLAS implementations:
+	Known quirks and specific BLAS implementations:
+
+	Compiler dependence
+	-------------------
+	In general, you need a version of the BLAS which was compiled
+	by the Fortran compiler you plan to use. Sometimes it is
+	possible to get around this restrictions by linking in
+	additional libraries, as shown in some of the examples listed
+	below.
 
 	Intel's  "math core library" libmkl:
 	------------------------------------
-
 	Make sure to also link with libguide, this can be achieved by the
 	following configure switches: