Update numpy_guide.rst

doc/numpy_guide.rst

@@ -141,6 +141,16 @@ and is not named :func:`acos` like in the :mod:`math` module).
 The definition of the mathematical quantities calculated by these
 functions is available in the documentation for  :mod:`uncertainties.umath`.
 
+.. index:: Numbers with uncertainties from samples
+
+Numbers with uncertainties from samples
+---------------------------------------
+
+Numbers with uncertainties can be found from samples of numbers 
+without uncertainties using :func:`ufloat_from_sample`. This is
+an estimate on the true value of the number and its uncertainty,
+and so it works best for large samples that are normally dristobuted.
+
 .. index::
    pair: testing and operations (in arrays); NaN