Add language definition for R

[R](https://en.wikipedia.org/wiki/R_(programming_language))

Comments are simply started with a `#`

syntax.json

@@ -600,5 +600,14 @@
         "pattern": "#"
       }
     ]
+  },
+  {
+    "language": "R",
+    "markers": [
+      {
+        "type": "line",
+        "pattern": "#"
+      }
+    ]
   }
 ]