Update 9control.tex with link to richards growth curve vignette (#270)

9control.tex

@@ -518,7 +518,7 @@
 
 When $A_1$ is greater than the youngest age in the model, some combinations of Richards growth parameters can lead to undefined (NaN) predicted length for the younger ages. The choice of $A_1$ and $A_2$ will affect the possible growth curve shapes.
 
-The SS3 website includes a vignette providing further technical insights for using the Richards growth model in Stock Synthesis.
+The SS3 website includes \href{https://nmfs-ost.github.io/ss3-website/qmds/richards_growth_curve.html}{a vignette} providing further technical insights for using the Richards growth model in Stock Synthesis.
 
 
 \myparagraph{Mean size-at-maximum age}