Mingun trunk: couple of minor tweaks

Hi,

Thanks for your work; here's a few minor corrections re README documentation et al.


**Off topic**: I also got your annotations work and used it selectively enable cache check+store code per rule, which speeds up `--cache` generated grammars; the whole is available in https://github.com/GerHobbelt/pegjs gh-pages branch if you are interested to see your `@annotations` (in the form of `@nocache`) at work. :-)