Fixed typographical erros in the documentation

Used the RETF rules provided by Wikipedia to fix some typographical
errors in the Markdown files of the documentation with the following
script:

https://github.com/openstack/openstack-doc-tools/tree/master/cleanup/retf

Docker-DCO-1.1-Signed-off-by: Christian Berendt <berendt@b1-systems.de> (github: berendt)