Kernel#require documentation is incomplete
The documentation for Kernel#require could benefit from additional description.
It does not describe what a return method of false means. Many people initially think that a return value of false means that the require method was unsuccessful. See, for example, http://stackoverflow.com/q/1250329/38765 and http://stackoverflow.com/q/1793693/38765 . So explaining that it merely means that the library has already been loaded would be useful.
Mentioning that a LoadError is raised if unsuccessful would also be nice.
As a side issue, "it's" is used when it should be "its". The former means "it is", while the latter mean "something belonging to it".