Cross-reference allusion to more detailed lifetime introduction.

[nejucomo]

The borrowed pointers tutorial section 5 Borrowing managed boxes and rooting contains this sentence:

"We'll be discussing lifetimes more in the examples to come, and a more thorough introduction is also available."

Where is the more thorough introduction? Is it in the same document or another? Please add a link.

[steveklabnik]

Currently the tutorial is the most thorough introduction.

[pnkfelix]

part of #11755

[steveklabnik]

This sentence is now gone: http://doc.rust-lang.org/guide-lifetimes.html

This should be closed.