Improved documentation of stacked and lightweight branches
These patches improve the User Guide's documentation of stacked and lightweight branches.
Section "1.2.6 Putting the concepts together" should mention stacked branches and the difference between them and lightweight branches. It should also contain links to further details of the common scenarios.
Section "5.3.4 Getting a lightweight checkout" should mention stacked branches as an option, and should link to all the options, not just some of them. It should also clarify that lightweight only applies to checkouts, not to arbitrary branches.