Fixed username links in the performance guide
Fixed username links in the performance guide

These would end up being rendered as:

    <a href="...">@yorickpeterse</a>
    <a href="...">@yorickpeterse</a>

[ci skip]

allysonbarros/gitlabhq,icedwater/gitlabhq,Soullivaneuh/gitlabhq,mr-dxdy/gitlabhq,martijnvermaat/gitlabhq,mmkassem/gitlabhq,martijnvermaat/gitlabhq,dreampet/gitlab,daiyu/gitlab-zh,darkrasid/gitlabhq,iiet/iiet-git,htve/GitlabForChinese,jirutka/gitlabhq,dreampet/gitlab,darkrasid/gitlabhq,openwide-java/gitlabhq,jirutka/gitlabhq,dreampet/gitlab,daiyu/gitlab-zh,mmkassem/gitlabhq,htve/GitlabForChinese,stoplightio/gitlabhq,axilleas/gitlabhq,martijnvermaat/gitlabhq,dreampet/gitlab,stoplightio/gitlabhq,SVArago/gitlabhq,jirutka/gitlabhq,icedwater/gitlabhq,daiyu/gitlab-zh,allysonbarros/gitlabhq,dplarson/gitlabhq,t-zuehlsdorff/gitlabhq,mr-dxdy/gitlabhq,t-zuehlsdorff/gitlabhq,shinexiao/gitlabhq,icedwater/gitlabhq,axilleas/gitlabhq,mr-dxdy/gitlabhq,iiet/iiet-git,t-zuehlsdorff/gitlabhq,t-zuehlsdorff/gitlabhq,SVArago/gitlabhq,dplarson/gitlabhq,stoplightio/gitlabhq,screenpages/gitlabhq,Soullivaneuh/gitlabhq,larryli/gitlabhq,darkrasid/gitlabhq,shinexiao/gitlabhq,shinexiao/gitlabhq,htve/GitlabForChinese,allysonbarros/gitlabhq,Soullivaneuh/gitlabhq,axilleas/gitlabhq,dplarson/gitlabhq,openwide-java/gitlabhq,darkrasid/gitlabhq,icedwater/gitlabhq,shinexiao/gitlabhq,larryli/gitlabhq,iiet/iiet-git,larryli/gitlabhq,mmkassem/gitlabhq,mr-dxdy/gitlabhq,screenpages/gitlabhq,htve/GitlabForChinese,SVArago/gitlabhq,stoplightio/gitlabhq,Soullivaneuh/gitlabhq,screenpages/gitlabhq,dplarson/gitlabhq,LUMC/gitlabhq,LUMC/gitlabhq,mmkassem/gitlabhq,larryli/gitlabhq,screenpages/gitlabhq,jirutka/gitlabhq,martijnvermaat/gitlabhq,openwide-java/gitlabhq,LUMC/gitlabhq,LUMC/gitlabhq,SVArago/gitlabhq,iiet/iiet-git,allysonbarros/gitlabhq,openwide-java/gitlabhq,axilleas/gitlabhq,daiyu/gitlab-zh