Add reference for Teixeira water diffusion model

Code/Mantid/docs/source/fitfunctions/TeixeiraWater.rst

@@ -9,9 +9,13 @@ TeixeiraWater
 Description
 -----------
 
-Teixeira's model for water. Models the Q dependence of the QENS line width (Gamma (hwhm)), diffusion coefficients (D), 
-residence times (tau) and jump lengths (length) to extract the associated long range diffusive
-motions of molecules. The this model (1961) has the form:
+Teixeira's model for water [1]_.
+
+Models the Q dependence of the QENS line width (Gamma (hwhm)), diffusion
+coefficients (D), residence times (tau) and jump lengths (length) to extract the
+associated long range diffusive motions of molecules.
+
+This model (1961) has the form:
 
 .. math:: Gamma(Q) = D*Q^2/(1 + D*Q^2*tau)
 
@@ -19,6 +23,11 @@ motions of molecules. The this model (1961) has the form:
 
 .. properties::
 
+References
+----------
+
+.. [1] J. Teixeira, M.-C. Bellissent-Funel, S. H. Chen, and A. J. Dianoux. `Phys. Rev. A, 31:1913–1917 <http://dx.doi.org/10.1103/PhysRevA.31.1913>`__
+
 .. categories::
 
 .. sourcelink::