BLAS/LAPACK API: add a note about what is available in the users documentation

doc/user/chapters/using.org

@@ -858,6 +858,20 @@
        * *Map functions*
          * map: apply a user operator on each tile of the matrix
 
+     In addition, all *BLAS 2/3 routines* (gemm, hemm, her2k, herk,
+     lauum, symm, syr2k, syrk, trmm, trsm) can be called using an
+     equivalent of the (C)BLAS/LAPACK(E) API. The parameters are the
+     same and the user just has to add *CHAMELEON_* to the standard name
+     of the routine. For example, in C
+     #+begin_src
+     CHAMELEON_Init(4,0);
+     CHAMELEON_cblas_dgemm(CblasColMajor, CblasNoTrans, CblasNoTrans,
+                           N, NRHS, N, 1.0, A, N, X, N, -1.0, B, N);
+     CHAMELEON_Finalize();
+     #+end_src
+     In Fortran, the function names are for example: ~CHAMELEON_blas_dgemm~
+     instead of ~DGEMM~ and ~CHAMELEON_lapack_dlauum~ instead of ~DLAUUM~.
+
 **** Options routines
      <<sec:options_routines>>