Minor Text Fix

See the general Documentation guidelines http://docs.gitlab.com/ce/development/doc_styleguide.html

What does this MR do?

Minor text fix in gitlab-ce->doc->user-> project->wiki->index.md from

"Wikis are very convenient if you don't want to keep **you** documentation in your
repository, but you do want to keep it in the same project where your code
resides."

to

"Wikis are very convenient if you don't want to keep **your** documentation in your
repository, but you do want to keep it in the same project where your code
resides."