doc: add isosphere implementation source link

src/icosphere.hpp

@@ -23,6 +23,8 @@ private:
 	std::vector<float> _vertices;
 	std::vector<unsigned int> _indices;
 
+    // Generating an isosphere
+    // https://schneide.blog/2016/07/15/generating-an-icosphere-in-c/
 	struct Triangle
 	{
 		int vertex[3];