Clearify when to use a specific CheckCode

An example of the biggest confusion module developers face is not actually knowing the difference between Detected vs Appears vs Vulnerable. For example: a module might flag something as a vulnerable by simply doing a banner check, but this is often unreliable because either 1) that banner can be fooled, or 2) the patch does not actually update the banner. More reasons may apply. Just because the banner LOOKS vulnearble doesn't mean it is.

Verification:
- [ ] Read and make sure the descriptions make sense.