add description on gutil.env in readme

gutil.env.type is misunderstanding so i added a comment to show how gulp should be called to make gutil.env work as needed
Trimming contents of distributed npm package.
Keep deployments as small as they can be.

https://www.npmjs.org/doc/developers.html#Keeping-files-out-of-your-package
Use "path.normalize" instead of "path.join"
Merge pull request #47 from pandell/fix-tests

Use "path.normalize" instead of "path.join"
Merge pull request #43 from CaleyD/master

Trimming contents of distributed npm package.
Merge pull request #38 from safareli/patch-1

add description on gutil.env in readme