small fix to glibc wiki (FAQ)

[Florian Weimer]

On 08/14/2017 01:31 PM, Ivo Raisr wrote:
> In glibc wiki, document "FAQ", paragraph "What version of the Linux
> kernel headers should be used?", the link to "kernel documentation" no
> longer works.
> 
> It has been moved to:
> http://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/kbuild/headers_install.txt

Thanks for the suggestion.  Fixed.

Florian