Updated README with current test coverage

  This should be updated periodically as new features are added and
tests written.

README.md

@@ -1,3 +1,13 @@
 # endless-edit
 
-Edit Endless Sky saves with Go!
+Edit Endless Sky saves with Go!
+
+# Test Coverage:
+
+> 87.8% of statements
+
+| File | Percent Coverage |
+|------|------------------|
+| node.go | 82.7% |
+| parser.go | 86.7% |
+| utils.go | 100.0% |