Add missing entry to the contributing guide TOC.
Add missing entry to the contributing guide TOC.

And add links to UI in the browser.

gares/coq,gares/coq,Zimmi48/coq,ejgallego/coq,Zimmi48/coq,Matafou/coq,JasonGross/coq,SkySkimmer/coq,coq/coq,coq/coq,SkySkimmer/coq,Zimmi48/coq,gares/coq,JasonGross/coq,JasonGross/coq,silene/coq,ejgallego/coq,coq/coq,Matafou/coq,Matafou/coq,ejgallego/coq,silene/coq,gares/coq,SkySkimmer/coq,silene/coq,coq/coq,gares/coq,SkySkimmer/coq,Zimmi48/coq,ejgallego/coq,JasonGross/coq