Fix typos in documentation of message format.
Fix typos in documentation of message format.

Signed-off-by: Michael Handler <331a76cd0f162b0218893a3dfa4df5a8bf659d1e@fullstop.at>

tobster/openengsb,openengsb/openengsb,openengsb/openengsb,tobster/openengsb,openengsb/openengsb,openengsb/openengsb,tobster/openengsb,openengsb/openengsb,openengsb/openengsb,tobster/openengsb