Design document for WaitSet

## Brief feature description

Many examples and some other readmes refer to the WaitSet example readme. It would be better to have a design document for the WaitSet to link to. This should also include the [Glossary](https://github.com/eclipse-iceoryx/iceoryx/tree/master/iceoryx_examples/waitset#glossary).

Start by reading the WaitSet example README under iceoryx_examples/waitset, including its Glossary, and identify the existing examples and READMEs that refer to it. Create a design document covering the WaitSet and the Glossary, then verify that the relevant references can link to the new document.

Written by the indexing model from the issue text.