Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/jest-leak-detector/README.md

@@ -0,0 +1,22 @@
+# jest-leak-detector
+
+Module for verifying whether an object has been garbage collected or not.
+
+Internally creates a weak reference to the object, and forces garbage collection to happen. If the reference is gone, it meant no one else was pointing to the object.
+
+## Example
+
+```javascript
+let reference = {};
+
+const detector = new LeakDetector(reference);
+
+// Reference is held in memory.
+console.log(detector.isLeaked()); // true
+
+// We destroy the only reference to the object.
+reference = null;
+
+// Reference is gone.
+console.log(detector.isLeaked()); // false
+```