Show help text about semver with grunt release:help

[kewisch]

I'm sometimes unsure when to do a major/minor/patch release. It would be nice to add a simple task release:help that shows the semver intro:

    MAJOR version when you make incompatible API changes,
    MINOR version when you add functionality in a backwards-compatible manner, and
    PATCH version when you make backwards-compatible bug fixes.

[drublic]

Good idea. Sounds good for me. Can you open a pull request?

[kewisch]

How is this? Let me know if you'd like anything changed.