Fix small issues in documentation and code

Matteo Franchin requested to merge readme_and_warn_fix into master

A couple of details in the installation instructions needed updating. Also fixed a warning message due to a missing return statement (the return value is currently not used in calls to the function).

Signed-off-by: Matteo Franchin Change-Id: I715b954579253e664ebe01f757587e0602ad82e7

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