Add block comment support for Rust

syntax.json

@@ -436,6 +436,13 @@
       {
         "type": "line",
         "pattern": "//"
+      },
+      {
+        "type": "block",
+        "pattern": {
+          "start": "/\\*",
+          "end": "\\*/"
+        }
       }
     ]
   }