add Rakefile Path section to rakefile.rdoc
about environment variable persistance in doc
fix my own typos
fix example
Merge branch 'docs' of https://github.com/CLUSTERfoo/rake into docs

* 'docs' of https://github.com/CLUSTERfoo/rake:
  fix example
  fix my own typos
  about environment variable persistance in doc
  add Rakefile Path section to rakefile.rdoc
Minor tweeks to rakefile document changes.