Add example with build directory outside of source directory

Background

A left over item following the merge of !776 (merged)

This item describes Technical debt.

See for !776 (comment 107972976) the original comment.

Task description

Add an example about "How to place your build directory outside of the source directory" example, which might contain multiple elements to show how to do it with cmake or autotools.

Acceptance Criteria

There is an example in doc/examples showing how to place the build directory of an element outside of it's source directory.

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