Update GSOC vignettes to be incorporated in RCy3

[jooolia]

Update https://github.com/jooolia/gsoc_Rcy3_vignettes/blob/master/tara_oceans_co-occurence_net_RCy3_vignette.md
https://github.com/jooolia/gsoc_Rcy3_vignettes/blob/master/chemviz_vignette.md so that they can be incorporated into RCy3.