docs: Add URL link for Numo::Gnuplot

kozo2 · web-flow · commit 0b6c8d7b567b · 2019-01-12T01:20:49.000+09:00
diff --git a/examples/graph.md b/examples/graph.md
@@ -1,6 +1,6 @@
 # Graph generation example
 
-## With Numo::Gnuplot
+## With [Numo::Gnuplot](https://github.com/ruby-numo/numo-gnuplot)
 
 `Rubydown::RbMarkPlot` is extended class of `Numo::Gnuplot`
 
