message: spectests: update README with --skip-validation
diff: @@ -14,6 +14,12 @@ It can then be executed:
  $ bin/fizzy-spectests <test directory>
  ```
  +This will execute all test cases, but since Fizzy does not implement the complete validation specification, most of
  +those cases will fail. It is possible to skip them:
  +```sh
  +$ bin/fizzy-spectests --skip-validation <test directory>
  +```
  +
  ## Preparing tests
  Fizzy uses the official WebAssembly "[spec tests]", albeit not directly.
  