Added 'fma' function to shader docs

tutorials/shading/shading_reference/shading_language.rst

@@ -761,6 +761,8 @@ When vec_type (float), vec_int_type, vec_uint_type, vec_bool_type nomenclature i
 +------------------------------------------------------------------------+---------------------------------------------------------------+
 | vec_type **mix** (vec_type a, vec_type b, bvec_type c)                 | Linear interpolate (boolean-vector selection)                 |
 +------------------------------------------------------------------------+---------------------------------------------------------------+
+| vec_type **fma** (vec_type a, vec_type b, vec_type c)                  | Performs a fused multiply-add operation: ``(a * b + c)``      |
++------------------------------------------------------------------------+---------------------------------------------------------------+
 | vec_type **step** (vec_type a, vec_type b)                             | ``b[i] < a[i] ? 0.0 : 1.0``                                   |
 +------------------------------------------------------------------------+---------------------------------------------------------------+
 | vec_type **step** (float a, vec_type b)                                | ``b[i] < a ? 0.0 : 1.0``                                      |