Fixed build error 'WARNING: document isn't included in any toctree'
merged branch WouterJ/patch-3 (PR #185)

This PR was merged into the 2.1 branch.

Discussion
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Fixed build error 'WARNING: document isn't included in any toctree'

this should get merged into 2.2 and master aswell, I don't know if this is done automatically in this repo.

Commits
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fa3c528 Fixed build error 'WARNING: document isn't included in any toctree'