Fix typos in docs

[martinus]

Thanks for the PR! Note though that the documentation is created automatically from the sourcecode. So you'd have to update the wording in nanobench.h and regenerate the documentation (see src/docs/generate.sh). I'm on holiday for a week though so no more access to computers to do this.

[tocic]

Sorry, my bad. Fixed now. But didn't completely regenerate the root's docs, only affected files, because I have newer versions of the generate.sh's dependencies, so running it introduces too much noise in the commit diff + your future runs will rewrite it anyway. Of course, feel free to look at the PR when you'll have free time.