adding citations for CK test discussion (this fixes #171)

Author: cwehmeyer

manuscript/manuscript.tex

@@ -158,7 +158,7 @@ \subsection{Markov state models}
 \mathbf{P}(k \tau) = \mathbf{P}^k(\tau),
 \end{equation}
 where the left-hand side of the equation corresponds to an MSM estimated at lag time $k\tau$, where $k$ is an integer larger than~$1$, whereas the right-hand side of the equation is our estimated MSM transition probability matrix to the $k^\textrm{th}$ power.
-By assessing how well the approximated transition probability matrix adheres to the CK property, we can validate the appropriateness of the Markovian assumption for the model.
+By assessing how well the approximated transition probability matrix adheres to the CK property, we can validate the appropriateness of the Markovian assumption for the model~\cite{msm-jhp,noe-folding-pathways}.
 
 Once validated, the transition matrix can be decomposed into eigenvectors and eigenvalues.
 The highest eigenvalue, $\lambda_1(\tau)$, is unique and equal to $1$.