Update serialization-howto.markdown
Update serialization-howto.markdown

Just some grammar fixes.
maekitalo/cxxtools,OlafRadicke/cxxtools,maekitalo/cxxtools,OlafRadicke/cxxtools,OlafRadicke/cxxtools,maekitalo/cxxtools,maekitalo/cxxtools,OlafRadicke/cxxtools