Documentation for semantic annotation extension to Scala IDE

Documentation for semantic annotation extension to Scala IDE (task #1001989, https://github.com/scala-ide/scala-ide/pull/644)

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This doesn't work the way you would expect. An `'\ '` sequence is needed between the literal block and the `s` to get the effect you want:

```
``val``\ s, ``var``\ s, ``def``\ s and/or ``lazy val``\ s
```