docs(userguide): Added documentation for args

Author: Logan Grado

docs/userguide.rst

@@ -65,13 +65,14 @@ The :code:`solve` function has several optional arguments which the user may pro
 
   .. code-block:: python
   
-      pybobyqa.solve(objfun, x0, bounds=None, npt=None, rhobeg=None, 
-                  rhoend=1e-8, maxfun=None, nsamples=None, 
+      pybobyqa.solve(objfun, x0, args=(), bounds=None, npt=None,
+		  rhobeg=None, rhoend=1e-8, maxfun=None, nsamples=None, 
                   user_params=None, objfun_has_noise=False, 
                   scaling_within_bounds=False)
 
 These arguments are:
 
+* :code:`args` - a tuple of extra arguments passed to the objective function
 * :code:`bounds` - a tuple :code:`(lower, upper)` with the vectors :math:`a` and :math:`b` of lower and upper bounds on :math:`x` (default is :math:`a_i=-10^{20}` and :math:`b_i=10^{20}`). To set bounds for either :code:`lower` or :code:`upper`, but not both, pass a tuple :code:`(lower, None)` or :code:`(None, upper)`.
 * :code:`npt` - the number of interpolation points to use (default is :code:`2*len(x0)+1`). Py-BOBYQA requires :code:`n+1 <= npt <= (n+1)*(n+2)/2` for a problem with :code:`len(x0)=n`. Larger values are particularly useful for noisy problems.
 * :code:`rhobeg` - the initial value of the trust region radius (default is :math:`0.1\max(\|x_0\|_{\infty}, 1)`).