doc: Missing link in language design FAQ

[graue]

Section 1.7 of the language design FAQ, "No guaranteed tail-call optimization", appears to be missing a link, between the words "see" and "for":

see for a detailed explanation with references

@cmr, what's meant to go here?

[emberian]

https://mail.mozilla.org/pipermail/rust-dev/2013-April/003557.html