Added the first genetic infector gene, stretcher, and docs for it

Source/Genes/Diseases/Defs/GeneticInfectorExtension.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Verse;
+
+namespace RJW_Genes
+{
+    public class GeneticInfectorExtension : DefModExtension
+    {
+        public float infectionChance;
+
+        public List<string> infectionGenes;
+    }
+
+}