A few minor updates based on feedback from Justin and a few things I thought were missing.

* Moved autotools configure & build example out of "Getting Started Quickly (A Summary)" and into BuildingLLVMWithAutoTools.
* Removed the annotations that CMake is the recommended process and Autotools is alternate.
* Added brief documentation about build targets under "Getting Started Quickly..."
* Added Overview text to BuildingLLVMWithAutotools
* Fixed up a broken link.

llvm-svn: 232278