Add "unwanted coverage" to user documentation

[koppor]

I have a simple project setup.

### Chatting with AI
`req~ai.chat.new-message-based-on-previous~1`

            } else if (keyEvent.getCode() == KeyCode.UP) {
                // [impl->req~ai.chat.new-message-based-on-previous~1]

Now, I get

[unwanted coverage] ← impl~ai.chat.new-message-based-on-previous-2709826873~0

As beginner user, I expect that https://github.com/itsallcode/openfasttrace/blob/main/doc/user_guide.md days something about the case.

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Are the artifact types at https://github.com/itsallcode/openfasttrace/blob/main/doc/user_guide.md#specification-item-id hard-coded in the system?

It seems that they are hard-coded in the system. Then, the following sentence needs to be rewritten:

While not enforced by OFT the following strings are well established:

---

Maybe at https://github.com/itsallcode/openfasttrace/blob/main/doc/user_guide.md#writing-a-specification?

The solution to my concrete case is to add following to the requirement:

Needs: impl