add external icon on DOI link

src/Gargantext/Components/Document/Layout.purs

@@ -365,7 +365,11 @@ layoutWithContextNgramsCpt = here.component "layoutWithContextNgrams" cpt where
               , id: getIdName "doi" }
               [
                 if (TUV.validateURL doi) then
-                  H.a {classname: "", on: { click: goToURLInNewTab $ doi }} [ H.text doi ]
+                  H.a {classname: "", on: { click: goToURLInNewTab $ doi }} 
+                  [ 
+                    H.text doi 
+                  , H.i { className: "fa fa-external-link mx-1 small" } []
+                  ]
                 else
                   H.text doi
               ]