Alteration to OroRequirements.php related to Node

Alteration to check requirements for node(default) or what is in config

Detect whether a js engine is installed rather then just "node" based on the config settings
Update to the README.md to show below yaml for Ubuntu installs
```
oro_require_js:
    js_engine:  "nodejs"
```
This allows the checks to pass if an alternate js_engine is installed