Adding requested changes

I think a better link to use would be http://libcinder.org/images/logo.png - it is a static url, rather than one generated by doxygen (for the dead dev branch at that).

Period after "User Forum", and 'you can..' should be capitalized ("Be sure to check the User Forum. You can...").
Merge pull request #2 from claudiordgz/readme-mod

Adding requested changes