try to fix ref in docs

Author: Vincent Landau

docs/src/index.md

@@ -6,6 +6,6 @@ SpatialGraphs.jl is useful for turning spatial data into graphs. This can be
 useful for landscape connectivity analysis, hydrology, and other spatial
 network processes. AbstractSpatialGraphs are AbstractGraphs, methods from 
 LightGraphs.jl work right out of the box. 
-Go to [Graph Types](@ref) for more details on the graph types implemented in 
+Go to [Graph Types](@ref Graph Types in SpatialGraphs.jl) for more details on the graph types implemented in 
 this package.