Update mixture GCMC example readme

Added where to find the partial charges of the framework + force field (LJ) parameters in the SI of the referenced paper.

Examples/Bae-Mixture/readme.md

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 This is an example of using gRASPA for reproducing [Bae et al.](https://pubs.acs.org/doi/10.1021/la800555x) result.
 
 Please refer to [Figure 8 of this paper](https://pubs.acs.org/cms/10.1021/la800555x/asset/images/medium/la-2008-00555x_0002.gif). 
+
+# Force field parameters and partial charges
+* Please refer to the **Supplemental Information** of [Bae et al.](https://pubs.acs.org/doi/10.1021/la800555x)
+  * Partial charges of the framework atoms are in **Table S5 and Table S6**.
+  * Force field (LJ) parameters are in **Table S7 and Table S8**.